Securities - Securities Available for Sale in Unrealized Loss Position (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair value, Less than 12 months	$ 0	$ 240,461,000
Unrealized loss, Less than 12 months	0	(2,496,000)
Fair value, 12 months or more	0	69,333,000
Unrealized loss, 12 months or more	$ 0	(1,743,000)
Total Fair value		309,794,000
Total, unrealized loss		(4,239,000)
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, Less than 12 months		139,876,000
Unrealized loss, Less than 12 months		(1,654,000)
Fair value, 12 months or more		55,055,000
Unrealized loss, 12 months or more		(1,355,000)
Total Fair value		194,931,000
Total, unrealized loss		(3,009,000)
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, Less than 12 months		100,585,000
Unrealized loss, Less than 12 months		(842,000)
Fair value, 12 months or more		14,278,000
Unrealized loss, 12 months or more		(388,000)
Total Fair value		114,863,000
Total, unrealized loss		$ (1,230,000)