Fair Value Information - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Assets
Total cash and cash equivalents	$ 699,182	$ 106,097	$ 446,446	$ 105,768
Interest-earning balances due from depository institutions	91,272	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,248,032	2,368,646
Investment securities held-to-maturity	724,357	850,989
Total loans, net of allowance for loan losses	4,176,990	3,957,781
Deposits:
Noninterest-bearing	3,666,206	3,250,174
Interest-bearing	2,919,780	2,667,086
Junior subordinated debentures	25,774	25,774
Swaps	605,626	700,048
Carrying Value [Member]
Assets
Total cash and cash equivalents	699,182	106,097
Interest-earning balances due from depository institutions	91,272	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,248,032	2,368,646
Investment securities held-to-maturity	724,357	850,989
Total loans, net of allowance for loan losses	4,176,990	3,957,781
Swaps	15,161	9,344
Deposits:
Noninterest-bearing	3,666,206	3,250,174
Interest-bearing	2,919,780	2,667,086
Borrowings	590,465	736,704
Junior subordinated debentures	25,774	25,774
Swaps	15,161	9,344
Estimated Fair Value [Member]
Assets
Total cash and cash equivalents	699,182	106,097
Interest-earning balances due from depository institutions	91,272	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,248,032	2,368,646
Investment securities held-to-maturity	743,481	853,039
Total loans, net of allowance for loan losses	4,243,374	3,971,329
Swaps	15,161	9,344
Deposits:
Noninterest-bearing	3,666,206	3,250,174
Interest-bearing	2,919,677	2,666,186
Borrowings	590,342	736,575
Junior subordinated debentures	27,383	27,210
Swaps	15,161	9,344
Estimated Fair Value [Member] | Level 1 [Member]
Assets
Total cash and cash equivalents	699,182	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	3,666,206	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	91,272	32,691
FHLB stock	17,688	17,588
Investment securities available-for-sale	2,248,032	2,368,646
Investment securities held-to-maturity	742,006	851,186
Total loans, net of allowance for loan losses	0	0
Swaps	15,161	9,344
Deposits:
Noninterest-bearing	0	0
Interest-bearing	2,919,677	2,666,186
Borrowings	590,342	736,575
Junior subordinated debentures	27,383	27,210
Swaps	15,161	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	1,475	1,853
Total loans, net of allowance for loan losses	4,243,374	3,971,329
Swaps	0	0
Deposits:
Noninterest-bearing	0	0
Interest-bearing	0	0
Borrowings	0	0
Junior subordinated debentures	0	0
Swaps	$ 0	$ 0