Securities - Securities Held to Maturity in Unrecognized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Held To Maturity Securities [Line Items]
Fair value, Less than 12 months		$ 22,723
Unrealized loss, Less than 12 months		(289)
Fair value, 12 months or more	$ 28,626	76,396
Unrealized loss, 12 months or more	(182)	(2,390)
Total fair value	28,626	99,119
Total unrealized loss	(182)	(2,679)
Mortgage-Backed GSE Securities: Residential [Member]
Schedule Of Held To Maturity Securities [Line Items]
Fair value, Less than 12 months		22,723
Unrealized loss, Less than 12 months		(289)
Fair value, 12 months or more	28,626	76,396
Unrealized loss, 12 months or more	(182)	(2,390)
Total fair value	28,626	99,119
Total unrealized loss	$ (182)	$ (2,679)