Annual report pursuant to Section 13 and 15(d)

Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail)

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Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]                      
Interest and dividend income $ 55,784 $ 53,862 $ 51,326 $ 48,349 $ 47,313 $ 44,325 $ 44,159 $ 42,674 $ 209,321 $ 178,471 $ 164,226
Interest expense 9,440 8,936 8,148 5,995 5,247 4,743 4,179 4,105 32,519 18,274 16,109
Net interest income before provision for loan and lease losses 46,344 44,926 43,178 42,354 42,066 39,582 39,980 38,569 176,802 160,197 148,117
Loan and lease loss provision (income) 220 269 422 (80) 151 (1,450) (1,515) (1,525) 831 (4,339) (11,614)
Non-interest income 7,680 8,816 9,702 7,217 8,067 8,674 9,373 6,961 33,415 33,075 47,602
Non-interest expense 29,258 28,660 28,944 27,240 25,955 28,337 27,863 26,068 114,102 108,223 115,328
Income before provision for income taxes 24,546 24,813 23,514 22,411 24,027 21,369 23,005 20,987      
Provision for income taxes 13,049 9,890 9,057 8,628 9,611 8,248 8,857 6,183 40,624 32,899 38,182
Net income $ 11,497 $ 14,923 $ 14,457 $ 13,783 $ 14,416 $ 13,121 $ 14,148 $ 14,804 $ 54,660 $ 56,489 $ 53,823
Basic earnings per share:                      
Basic earnings per share (in usd per share) $ 0.36 $ 0.46 $ 0.45 $ 0.43 $ 0.45 $ 0.41 $ 0.44 $ 0.46 $ 1.70 $ 1.76 $ 1.69
Diluted earnings per share:                      
Diluted earnings per share (in usd per share) $ 0.36 $ 0.46 $ 0.45 $ 0.43 $ 0.45 $ 0.41 $ 0.44 $ 0.46 $ 1.69 $ 1.75 $ 1.68