Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Mar. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Fair Value
Less Than 12 Months	$ 448,486	$ 174,022
12 Months or Longer	54,505	23,308
Total	$ 502,991	$ 197,330
Number of Securities | security	192	61
Unrealized Losses
Less Than 12 Months	$ 13,451	$ 977
12 Months or Longer	419	353
Total	13,870	1,330
Fair Value
Less Than 12 Months	5,894	2,561
12 Months or Longer	44	0
Total	5,938	2,561
Unrealized Losses
Less Than 12 Months	271	12
12 Months or Longer	0	0
Total	$ 271	$ 12
Number of Securities | security	8	4
U.S. Treasury and U.S. government agencies
Fair Value
Less Than 12 Months	$ 26,117	$ 4,966
12 Months or Longer	16,532	17,652
Total	$ 42,649	$ 22,618
Number of Securities | security	9	6
Unrealized Losses
Less Than 12 Months	$ 805	$ 29
12 Months or Longer	256	284
Total	1,061	313
Mortgage-backed securities, residential
Fair Value
Less Than 12 Months	215,618	84,137
12 Months or Longer	4,502	5,656
Total	$ 220,120	$ 89,793
Number of Securities | security	59	30
Unrealized Losses
Less Than 12 Months	$ 5,404	$ 471
12 Months or Longer	15	69
Total	5,419	540
Fair Value
Less Than 12 Months	5,784	2,561
12 Months or Longer	43	0
Total	5,827	2,561
Unrealized Losses
Less Than 12 Months	271	12
12 Months or Longer	0	0
Total	$ 271	$ 12
Number of Securities | security	5	4
Collateralized mortgage obligations, residential
Fair Value
Less Than 12 Months	$ 19,099	$ 23,858
12 Months or Longer	0	0
Total	$ 19,099	$ 23,858
Number of Securities | security	6	7
Unrealized Losses
Less Than 12 Months	$ 188	$ 22
12 Months or Longer	0	0
Total	188	22
Fair Value
Less Than 12 Months	110
12 Months or Longer	1
Total	111
Unrealized Losses
Less Than 12 Months	0
12 Months or Longer	0
Total	$ 0
Number of Securities | security	3
Mortgage-backed securities, multifamily
Fair Value
Less Than 12 Months	$ 1,841	1,943
12 Months or Longer	0	0
Total	$ 1,841	$ 1,943
Number of Securities | security	1	1
Unrealized Losses
Less Than 12 Months	$ 100	$ 0
12 Months or Longer	0	0
Total	100	0
Collateralized mortgage obligations, multifamily
Fair Value
Less Than 12 Months	2,131	2,527
12 Months or Longer	0	0
Total	$ 2,131	$ 2,527
Number of Securities | security	1	1
Unrealized Losses
Less Than 12 Months	$ 46	$ 2
12 Months or Longer	0	0
Total	46	2
Asset-backed securities
Fair Value
Less Than 12 Months	0	40,690
12 Months or Longer	33,471	0
Total	$ 33,471	$ 40,690
Number of Securities | security	4	6
Unrealized Losses
Less Than 12 Months	$ 0	$ 225
12 Months or Longer	148	0
Total	148	225
Obligations of states and political subdivisions
Fair Value
Less Than 12 Months	173,875	15,901
12 Months or Longer	0	0
Total	$ 173,875	$ 15,901
Number of Securities | security	106	10
Unrealized Losses
Less Than 12 Months	$ 6,848	$ 228
12 Months or Longer	0	0
Total	6,848	$ 228
Debt securities
Fair Value
Less Than 12 Months	9,805
12 Months or Longer	0
Total	$ 9,805
Number of Securities | security	6
Unrealized Losses
Less Than 12 Months	$ 60
12 Months or Longer	0
Total	$ 60