Fair Value Information - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Total cash and cash equivalents	$ 121,633	$ 106,097	$ 105,768	$ 94,693
Interest-earning balances due from depository institutions	47,848	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,270,466	2,368,646
Investment securities held-to-maturity	911,676	850,989
Total loans, net of allowance for loan losses	4,333,524	3,957,781
Swaps	5,783	9,344
Deposits:
Noninterest-bearing	3,673,541	3,250,174
Interest-bearing	2,636,139	2,667,086
Junior subordinated debentures	25,774	25,774
Swaps	608,811	700,048
Carrying Value [Member]
Assets
Total cash and cash equivalents	119,445	106,097
Interest-earning balances due from depository institutions	2,188	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,270,466	2,368,646
Investment securities held-to-maturity	911,676	850,989
Total loans, net of allowance for loan losses	4,333,524	3,957,781
Swaps	5,783	9,344
Deposits:
Noninterest-bearing	3,673,541	3,250,174
Interest-bearing	2,636,139	2,667,086
Borrowings	656,028	736,704
Junior subordinated debentures	25,774	25,774
Swaps	5,783	9,344
Estimated Fair Value [Member]
Assets
Total cash and cash equivalents	119,445	106,097
Interest-earning balances due from depository institutions	2,188	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,270,466	2,368,646
Investment securities held-to-maturity	897,374	853,039
Total loans, net of allowance for loan losses	4,306,225	3,971,329
Swaps	5,783	9,344
Deposits:
Noninterest-bearing	3,673,541	3,250,174
Interest-bearing	2,634,443	2,666,186
Borrowings	655,820	736,575
Junior subordinated debentures	18,463	27,210
Swaps	5,783	9,344
Estimated Fair Value [Member] | Level 1 [Member]
Assets
Total cash and cash equivalents	119,445	106,097
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	3,673,541	3,250,174
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	2,188	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,270,466	2,368,646
Investment securities held-to-maturity	897,374	851,186
Total loans, net of allowance for loan losses	0	0
Swaps	5,783	9,344
Deposits:
Noninterest-bearing	0	0
Interest-bearing	2,634,443	2,666,186
Borrowings	655,820	736,575
Junior subordinated debentures	0	0
Swaps	5,783	9,344
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	1,853
Total loans, net of allowance for loan losses	4,306,225	3,971,329
Swaps	0	0
Deposits:
Noninterest-bearing	0	0
Interest-bearing	0	0
Borrowings	0	0
Junior subordinated debentures	18,463	27,210
Swaps	$ 0	$ 0