Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Summary of Stock Option Transactions under Plans (Detail)

v2.4.1.9
Share-based Compensation - Summary of Stock Option Transactions under Plans (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Options outstanding at end of period 603,872us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber    
Number of Shares, Options exercisable at end of period 224,766us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber    
Weighted-Average Exercise Price Per Share, Options outstanding at beginning of period $ 28.09us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 37.44us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 81.27us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options granted $ 21.30us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice $ 16.43us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice $ 12.54us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options exercised $ 12.42us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 11.37us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 8.00us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options forfeited $ 14.64us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice $ 12.50us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice $ 8.61us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options expired $ 106.70us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice $ 81.20us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice $ 98.76us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options outstanding at end of period $ 23.78us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 28.09us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 37.44us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Weighted-Average Exercise Price Per Share, Options exercisable at end of period $ 33.35us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice $ 59.77us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice $ 66.19us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
Stock option awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, options outstanding at beginning of period 546,595us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
342,950us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
143,325us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options granted 158,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
305,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
221,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options exercised (37,569)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(46,113)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(1,250)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options forfeited (30,917)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(36,566)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(5,375)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options expired (32,237)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(18,676)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
(15,500)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options outstanding at end of period 603,872us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
546,595us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
342,950us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Number of Shares, Options exercisable at end of period 224,766us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
154,970us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
159,762us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember