Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 465,271	$ 663,576
Less Than 12 Months, Unrealized Losses	1,898	4,324
12 Months or Longer, Fair Value	0	399,895
12 Months or Longer, Unrealized Losses	0	6,921
Total, Fair Value	465,271	1,063,471
Total, Unrealized Losses	1,898	11,245
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	162,870	24,420
Less Than 12 Months, Unrealized Losses	866	72
12 Months or Longer, Fair Value	0	9,976
12 Months or Longer, Unrealized Losses	0	24
Total, Fair Value	162,870	34,396
Total, Unrealized Losses	866	96
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	0	25,251
Less Than 12 Months, Unrealized Losses	0	303
Total, Fair Value	0	25,251
Total, Unrealized Losses	0	303
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	302,401	613,905
Less Than 12 Months, Unrealized Losses	1,032	3,949
12 Months or Longer, Fair Value	0	389,919
12 Months or Longer, Unrealized Losses	0	6,897
Total, Fair Value	302,401	1,003,824
Total, Unrealized Losses	$ 1,032	$ 10,846