Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments, Not Previously Presented (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, federal funds sold, and money market investments	$ 255,519	$ 219,818	$ 239,963	$ 206,723
Investment securities - held-to-maturity	745,090	872,111
Federal Home Loan Bank/Federal Reserve Bank stock	101,716	86,146
FDIC indemnification asset		9,030	$ 20,603
Accrued interest receivable	81,381	69,098
Noninterest-bearing demand deposits	3,016,093	2,488,855
Time deposits	1,468,108	1,000,067
Federal funds purchased and interbank borrowings	213,003	291,090
Securities sold under agreements to repurchase	367,052	387,409
Other borrowings	1,353,092	1,023,491
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, federal funds sold, and money market investments	255,519	219,818
Accrued interest receivable	16	29
Noninterest-bearing demand deposits	3,016,093	2,488,855
NOW, savings, and money market deposits	6,259,052	4,911,938
Federal funds purchased and interbank borrowings	213,003	291,090
Securities sold under agreements to repurchase	317,052	337,409
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued interest receivable	22,880	22,821
Time deposits	1,460,778	998,878
Securities sold under agreements to repurchase	50,612	51,370
Other borrowings	217,647	201,138
Accrued interest payable	5,979	4,859
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial	1,971,296	1,829,824
Commercial real estate	3,400,365	1,946,163
Residential real estate	2,228,542	1,745,248
Consumer credit	1,974,180	1,587,879
FDIC indemnification asset		5,700
Accrued interest receivable	58,485	46,248
Federal Home Loan Bank advances	1,360,599	1,029,779
Standby letters of credit	315	429
Commitments to extend credit	2,527	2,364
U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	40,131	142,864
U.S. Government-Sponsored Entities and Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	40,558	145,763
Mortgage-Backed Securities - Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	10,640	16,042
Mortgage-Backed Securities - Agency [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	10,940	16,604
States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	694,319	713,205
States and Political Subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	732,674	767,050
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, federal funds sold, and money market investments	255,519	219,818
Federal Home Loan Bank/Federal Reserve Bank stock	101,716	86,146
Commercial	1,895,618	1,788,593
Commercial real estate	3,112,680	1,852,979
Residential real estate	2,085,887	1,659,284
Consumer credit	1,866,519	1,595,316
FDIC indemnification asset		9,030
Accrued interest receivable	81,381	69,098
Noninterest-bearing demand deposits	3,016,093	2,488,855
NOW, savings, and money market deposits	6,259,052	4,911,938
Time deposits	1,468,108	1,000,067
Federal funds purchased and interbank borrowings	213,003	291,090
Securities sold under agreements to repurchase	367,052	387,409
Federal Home Loan Bank advances	1,353,092	1,023,491
Other borrowings	218,939	218,256
Accrued interest payable	5,979	4,859
Standby letters of credit	315	429
Carrying Value [Member] | U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	40,131	142,864
Carrying Value [Member] | Mortgage-Backed Securities - Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	10,640	16,042
Carrying Value [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - held-to-maturity	$ 694,319	$ 713,205