Fair Value Information - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Total cash and cash equivalents	$ 137,196	$ 119,445
Interest-earning balances due from depository institutions	20,521	47,848
FHLB stock	17,688	17,688
Investment securities available-for-sale	2,175,648	2,270,466
Investment securities held-to-maturity	848,382	911,676
Total loans, net of allowance for loan losses	4,685,793	4,333,524
Deposits:
Noninterest-bearing	3,908,809	3,673,541
Interest-bearing	2,699,287	2,636,139
Junior subordinated debentures	25,774	25,774
Swaps	459,888	608,811
Carrying Value [Member]
Assets
Total cash and cash equivalents	143,790	119,445
Interest-earning balances due from depository institutions	20,521	2,188
FHLB stock	17,688	17,688
Investment securities available-for-sale	2,175,648	2,270,466
Investment securities held-to-maturity	848,382	911,676
Total loans, net of allowance for loan losses	4,685,793	4,333,524
Swaps	4,819	5,783
Deposits:
Noninterest-bearing	3,908,809	3,673,541
Interest-bearing	2,699,287	2,636,139
Borrowings	518,069	656,028
Junior subordinated debentures	25,774	25,774
Swaps	4,819	5,783
Estimated Fair Value [Member]
Assets
Total cash and cash equivalents	143,790	119,445
Interest-earning balances due from depository institutions	20,567	2,188
FHLB stock	17,688	17,688
Investment securities available-for-sale	2,175,648	2,270,466
Investment securities held-to-maturity	842,050	897,374
Total loans, net of allowance for loan losses	4,619,896	4,306,225
Swaps	4,819	5,783
Deposits:
Noninterest-bearing	3,908,809	3,673,541
Interest-bearing	2,697,349	2,634,443
Borrowings	517,827	655,820
Junior subordinated debentures	18,260	18,463
Swaps	4,819	5,783
Estimated Fair Value [Member] | Level 1 [Member]
Assets
Total cash and cash equivalents	143,790	119,445
Interest-earning balances due from depository institutions	0	0
FHLB stock	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:
Noninterest-bearing	3,908,809	3,673,541
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	20,567	2,188
FHLB stock	17,688	17,688
Investment securities available-for-sale	2,175,648	2,270,466
Investment securities held-to-maturity	842,050	897,374
Total loans, net of allowance for loan losses	0	0
Swaps	4,819	5,783
Deposits:
Noninterest-bearing	0	0
Interest-bearing	2,697,349	2,634,443
Borrowings	517,827	655,820
Junior subordinated debentures	0	0
Swaps	4,819	5,783
Estimated Fair Value [Member] | Level 3 [Member]
Assets
Total cash and cash equivalents	0	0
Interest-earning balances due from depository institutions	0	0
FHLB stock	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Total loans, net of allowance for loan losses	4,619,896	4,306,225
Swaps	0	0
Deposits:
Noninterest-bearing	0	0
Interest-bearing	0	0
Borrowings	0	0
Junior subordinated debentures	18,260	18,463
Swaps	$ 0	$ 0