Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 1,113,231	$ 636,077
Less Than 12 Months, Unrealized Losses	22,340	6,798
12 Months or Longer, Fair Value	58,535	123,864
12 Months or Longer, Unrealized Losses	1,852	2,926
Total, Fair Value	1,171,766	759,941
Total, Unrealized Losses	24,192	9,724
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	59,219	9,859
Less Than 12 Months, Unrealized Losses	527	141
Total, Fair Value	59,219	9,859
Total, Unrealized Losses	527	141
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	1,008,960	626,218
Less Than 12 Months, Unrealized Losses	20,725	6,657
12 Months or Longer, Fair Value	58,535	123,864
12 Months or Longer, Unrealized Losses	1,852	2,926
Total, Fair Value	1,067,495	750,082
Total, Unrealized Losses	22,577	$ 9,583
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	45,052
Less Than 12 Months, Unrealized Losses	1,088
Total, Fair Value	45,052
Total, Unrealized Losses	$ 1,088