Securities - Securities with Unrealized Losses Aggregated by Investment Category and Length of Time that Individual Securities have been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 136,060	$ 117,835
Less than 12 Months, Unrealized Loss	(1,311)	(961)
12 Months or More, Fair Value	129,088	240,321
12 Months or More, Unrealized Loss	(3,012)	(7,543)
Total, Fair Value	265,148	358,156
Total, Unrealized Loss	(4,323)	(8,504)
U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	44,488	26,069
Less than 12 Months, Unrealized Loss	(263)	(149)
12 Months or More, Fair Value	37,250	85,016
12 Months or More, Unrealized Loss	(270)	(2,070)
Total, Fair Value	84,738	111,085
Total, Unrealized Loss	(533)	(2,219)
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	19,065	16,398
Less than 12 Months, Unrealized Loss	(167)	(179)
12 Months or More, Fair Value	3,134	12,363
12 Months or More, Unrealized Loss	(62)	(223)
Total, Fair Value	22,199	28,761
Total, Unrealized Loss	(229)	(402)
Residential and Multi-Family Mortgage [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	69,507	70,360
Less than 12 Months, Unrealized Loss	(881)	(603)
12 Months or More, Fair Value	50,734	99,397
12 Months or More, Unrealized Loss	(1,068)	(2,202)
Total, Fair Value	120,241	169,757
Total, Unrealized Loss	(1,949)	(2,805)
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	5,008
Less than 12 Months, Unrealized Loss	0	(30)
12 Months or More, Fair Value	8,477	7,935
12 Months or More, Unrealized Loss	(936)	(1,470)
Total, Fair Value	8,477	12,943
Total, Unrealized Loss	(936)	(1,500)
Pooled SBA [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Fair Value	28,500	34,608
12 Months or More, Unrealized Loss	(649)	(1,560)
Total, Fair Value	28,500	34,608
Total, Unrealized Loss	(649)	(1,560)
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Fair Value	993	1,002
12 Months or More, Unrealized Loss	(27)	(18)
Total, Fair Value	993	1,002
Total, Unrealized Loss	$ (27)	$ (18)