Fair Value of Financial Instruments - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities AFS	$ 782,277	$ 839,321	$ 892,129
Time deposits	2,120,969	1,457,939	1,176,758
Repurchase agreements with customers	70,011	65,578	55,999
Other borrowings	161,931	190,855	280,875
FDIC clawback payable	0	0	26,533
Subordinated debentures	117,403	64,950	64,950
Carrying Amount [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	514,890	150,203	110,688
Demand, savings and interest bearing transaction deposits	4,966,330	4,038,443	3,807,139
Repurchase agreements with customers	70,011	65,578	55,999
Carrying Amount [Member] | Level 1, 2 and 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities AFS	782,277	839,321	892,129
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases, net of ALLL	6,537,222	5,074,899	4,528,696
FDIC loss share receivable	0	0	50,679
FDIC clawback payable	0	0	26,533
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Time deposits	2,120,969	1,457,939	1,176,758
Other borrowings	161,931	190,855	280,875
Subordinated debentures	117,403	64,950	64,950
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	514,890	150,203	110,688
Demand, savings and interest bearing transaction deposits	4,966,330	4,038,443	3,807,139
Repurchase agreements with customers	70,011	65,578	55,999
Estimated Fair Value [Member] | Level 1, 2 and 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities AFS	782,277	839,321	892,129
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases, net of ALLL	6,469,690	5,042,831	4,480,221
FDIC loss share receivable	0	0	50,600
FDIC clawback payable	0	0	26,533
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Time deposits	2,142,807	1,463,590	1,177,108
Other borrowings	171,614	203,493	304,381
Subordinated debentures	$ 66,679	$ 39,103	$ 32,554