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	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 209,274	$ 117,835
Less than 12 Months, Unrealized Loss	(3,840)	(961)
12 Months or More, Fair Value	157,604	240,321
12 Months or More, Unrealized Loss	(5,061)	(7,543)
Total, Fair Value	366,878	358,156
Total, Unrealized Loss	(8,901)	(8,504)
U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	51,164	26,069
Less than 12 Months, Unrealized Loss	(825)	(149)
12 Months or More, Fair Value	55,559	85,016
12 Months or More, Unrealized Loss	(866)	(2,070)
Total, Fair Value	106,723	111,085
Total, Unrealized Loss	(1,691)	(2,219)
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	43,017	16,398
Less than 12 Months, Unrealized Loss	(637)	(179)
12 Months or More, Fair Value	4,285	12,363
12 Months or More, Unrealized Loss	(127)	(223)
Total, Fair Value	47,302	28,761
Total, Unrealized Loss	(764)	(402)
Residential and Multi-Family Mortgage [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	106,961	70,360
Less than 12 Months, Unrealized Loss	(2,338)	(603)
12 Months or More, Fair Value	58,665	99,397
12 Months or More, Unrealized Loss	(1,974)	(2,202)
Total, Fair Value	165,626	169,757
Total, Unrealized Loss	(4,312)	(2,805)
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	5,010	5,008
Less than 12 Months, Unrealized Loss	(24)	(30)
12 Months or More, Fair Value	8,210	7,935
12 Months or More, Unrealized Loss	(1,199)	(1,470)
Total, Fair Value	13,220	12,943
Total, Unrealized Loss	(1,223)	(1,500)
Pooled SBA [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3,122	0
Less than 12 Months, Unrealized Loss	(16)	0
12 Months or More, Fair Value	28,724	34,608
12 Months or More, Unrealized Loss	(876)	(1,560)
Total, Fair Value	31,846	34,608
Total, Unrealized Loss	(892)	(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	1,001	1,002
12 Months or More, Unrealized Loss	(19)	(18)
Total, Fair Value	1,001	1,002
Total, Unrealized Loss	$ (19)	$ (18)