Securities - Securities Held to Maturity in Unrecognized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Held To Maturity Securities [Line Items]
Fair value, Less than 12 months	$ 61,586	$ 64,756
Unrealized loss, Less than 12 months	(1,111)	(1,329)
Fair value, 12 months or more	25,532	26,426
Unrealized loss, 12 months or more	(1,312)	(1,287)
Total fair value	87,118	91,182
Total unrealized loss	(2,423)	(2,616)
Mortgage-Backed GSE Securities: Residential [Member]
Schedule Of Held To Maturity Securities [Line Items]
Fair value, Less than 12 months	55,341	57,340
Unrealized loss, Less than 12 months	(1,071)	(1,243)
Fair value, 12 months or more	25,532	26,426
Unrealized loss, 12 months or more	(1,312)	(1,287)
Total fair value	80,873	83,766
Total unrealized loss	(2,383)	(2,530)
States of the U.S. and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Fair value, Less than 12 months	6,245	7,416
Unrealized loss, Less than 12 months	(40)	(86)
Total fair value	6,245	7,416
Total unrealized loss	$ (40)	$ (86)