Quarterly report pursuant to Section 13 or 15(d)

Securities - Additional Information (Detail)

v3.3.0.814
Securities - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Investment Securities [Line Items]          
Other-than-temporary impairment charge     $ 0 $ 0 $ 0
Impairment charges on securities in continuous unrealized loss position for 12 months or longer $ 0   0   0
Net realized gains on sales of securities 2,048,000 $ 67,000 6,144,000 1,852,000  
Recognized in earnings resulting from the sale of securities 1,200,000 $ 23,000 2,000,000 $ 498,000  
Securities available for sale 669,340,000   669,340,000   1,060,717,000
Collateralized mortgage obligations [Member]          
Investment Securities [Line Items]          
Securities available for sale 116,314,000   116,314,000   188,047,000
Mortgage-backed securities [Member]          
Investment Securities [Line Items]          
Securities available for sale 324,504,000   $ 324,504,000   573,286,000
Mortgage-backed securities [Member] | Collateralized mortgage obligations [Member]          
Investment Securities [Line Items]          
Contractual maturities     2064    
Securities Pledged as Collateral [Member]          
Investment Securities [Line Items]          
Securities available for sale $ 71,600,000   $ 71,600,000   $ 76,200,000