Fair Value Information - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets
Total cash and cash equivalents	$ 1,525,299	$ 1,958,160	$ 705,739	$ 185,518
Investment securities available-for-sale	2,812,348	2,398,923
Investment securities held-to-maturity	1,086,984	578,626
Total loans, net of allowance for loan losses	8,221,252	8,255,116
Deposits:
Interest-bearing	4,500,816	4,281,114
Junior subordinated debentures	25,774	25,774
Swaps	521,038	469,587
Carrying Value [Member]
Assets
Total cash and cash equivalents	1,525,299	1,958,160
Interest-earning balances due from depository institutions	27,748	43,563
Investment securities available-for-sale	2,812,348	2,398,923
Investment securities held-to-maturity	1,086,984	578,626
Total loans, net of allowance for loan losses	8,221,252	8,255,116
Swaps	14,692	30,181
Deposits:
Interest-bearing	4,500,816	4,281,114
Borrowings	511,346	444,406
Junior subordinated debentures	25,774	25,774
Swaps	14,692	30,181
Estimated Fair Value [Member]
Assets
Total cash and cash equivalents	1,525,299	1,958,160
Interest-earning balances due from depository institutions	27,748	43,600
Investment securities available-for-sale	2,812,348	2,398,923
Investment securities held-to-maturity	1,085,481	604,223
Total loans, net of allowance for loan losses	8,231,707	8,256,178
Swaps	14,692	30,181
Deposits:
Interest-bearing	4,500,611	4,281,952
Borrowings	504,563	444,349
Junior subordinated debentures	20,351	19,431
Swaps	14,692	30,181
Estimated Fair Value [Member] | Level 1 [Member]
Assets
Total cash and cash equivalents	1,525,299	1,958,160
Interest-earning balances due from depository institutions	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Total loans, net of allowance for loan losses	0	0
Swaps	0	0
Deposits:
Interest-bearing	0	0
Borrowings	0	0
Junior subordinated debentures	0	0
Swaps	0	0
Estimated Fair Value [Member] | Level 2 [Member]
Assets
Total cash and cash equivalents	0	0
Interest-earning balances due from depository institutions	27,748	43,600
Investment securities available-for-sale	2,812,348	2,398,923
Investment securities held-to-maturity	1,085,481	604,223
Total loans, net of allowance for loan losses	0	0
Swaps	14,692	30,181
Deposits:
Interest-bearing	4,500,611	4,281,952
Borrowings	504,563	444,349
Junior subordinated debentures	0	0
Swaps	14,692	30,181
Estimated Fair Value [Member] | Level 3 [Member]
Assets
Total cash and cash equivalents	0	0
Interest-earning balances due from depository institutions	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Total loans, net of allowance for loan losses	8,231,707	8,256,178
Swaps	0	0
Deposits:
Interest-bearing	0	0
Borrowings	0	0
Junior subordinated debentures	20,351	19,431
Swaps	$ 0	$ 0