Securities Available for Sale - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2013 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale at carrying value	$ 614,824,000	$ 585,928,000
Amortized cost	957,938,000	1,061,461,000
Securities available for sale, at fair value	964,534,000	1,074,395,000
Proceeds from the sale of securities available for sale	14,005,000	25,033,000	$ 14,834,000
Gross gains	643,000	632,000
Recognized gains on calls on securities in available for sale portfolio	3,000	2,000
Losses related to calls	0	404,000
Proceeds from the calls	$ 212,095,000	$ 207,531,000	$ 351,472,000
Number of securities in an unrealized loss position | security	64	43
Gain on previously impaired securities	$ 59,000
Loss on previously impaired securities	365,000
Cumulative Credit Losses	1,700,000
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	100,111,000
Securities available for sale, at fair value	100,154,000
Proceeds from the sale of securities available for sale	14,005,000	$ 24,509,000
Proceeds from the calls	1,110,000	740,000
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	857,430,000	944,796,000
Securities available for sale, at fair value	863,861,000	957,257,000
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	397,000	397,000
Securities available for sale, at fair value	519,000	$ 524,000
Private Label Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 773,000
Number of securities in an unrealized loss position | security	3
Unrealized losses	$ 5,000