Securities - Held to Maturity with Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	$ 934,207	$ 123,538
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	5,194	628
Held to maturity securities, Losses 12 months or longer, Fair value	419,483	694,234
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	10,647	12,224
Held to maturity securities, Total, Fair value	1,353,690	817,772
Held to maturity securities, Total, Gross Unrealized Losses	15,841	12,852
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	349,635
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	1,589
Held to maturity securities, Losses 12 months or longer, Fair value		95,522
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses		162
Held to maturity securities, Total, Fair value	349,635	95,522
Held to maturity securities, Total, Gross Unrealized Losses	1,589	162
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	516,330	119,222
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	2,894	616
Held to maturity securities, Losses 12 months or longer, Fair value	370,756	540,607
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	9,782	10,930
Held to maturity securities, Total, Fair value	887,086	659,829
Held to maturity securities, Total, Gross Unrealized Losses	12,676	11,546
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	22,652	4,316
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	301	12
Held to maturity securities, Losses 12 months or longer, Fair value	48,727	58,105
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	865	1,132
Held to maturity securities, Total, Fair value	71,379	62,421
Held to maturity securities, Total, Gross Unrealized Losses	1,166	$ 1,144
U.S. Treasury and Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	45,590
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	410
Held to maturity securities, Total, Fair value	45,590
Held to maturity securities, Total, Gross Unrealized Losses	$ 410