Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 663,576	$ 207,932
Less Than 12 Months, Unrealized Losses	4,324	2,076
12 Months or Longer, Fair Value	399,895	1,369,175
12 Months or Longer, Unrealized Losses	6,921	55,810
Total, Fair Value	1,063,471	1,577,107
Total, Unrealized Losses	11,245	57,886
U.S. Treasury [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value		9,958
Less Than 12 Months, Unrealized Losses		2
Total, Fair Value		9,958
Total, Unrealized Losses		2
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	24,420	9,849
Less Than 12 Months, Unrealized Losses	72	42
12 Months or Longer, Fair Value	9,976	69,499
12 Months or Longer, Unrealized Losses	24	761
Total, Fair Value	34,396	79,348
Total, Unrealized Losses	96	803
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	25,251
Less Than 12 Months, Unrealized Losses	303
12 Months or Longer, Fair Value		49,987
12 Months or Longer, Unrealized Losses		2,065
Total, Fair Value	25,251	49,987
Total, Unrealized Losses	303	2,065
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	613,905	188,125
Less Than 12 Months, Unrealized Losses	3,949	2,032
12 Months or Longer, Fair Value	389,919	1,249,689
12 Months or Longer, Unrealized Losses	6,897	52,984
Total, Fair Value	1,003,824	1,437,814
Total, Unrealized Losses	$ 10,846	$ 55,016