Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Financial Assets
Trading securities		$ 3,418	$ 3,013
Investment securities available-for-sale		663,925	637,329
Investment securities held-to-maturity		467,372	475,134
FDIC indemnification asset		0	6,725	$ 15,195	$ 16,762
Gross asset value of derivatives		5,683	933
Financial Liabilities
Contractual deposits		1,663,906	1,747,318
Federal Home Loan Bank advances		400,849	460,898
Gross liability value of derivatives		3	110
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets
Cash and cash equivalents		182,020	144,696
Trading securities		0	0
Investment securities available-for-sale		0	0
Investment securities held-to-maturity		0	0
Loans, net		0	0
FDIC indemnification asset			0
Receivable from FDIC			0
Other earning assets	[1]	0	0
Gross asset value of derivatives		0	0
Total financial assets		182,020	144,696
Financial Liabilities
Non-contractual deposits		0	0
Contractual deposits		0	0
Federal Home Loan Bank advances		0	0
Short-term borrowings		0	0
Subordinated debentures		0	0
Gross liability value of derivatives		0	0
Total financial liabilities		0	0
Significant Other Observable Inputs (Level 2)
Financial Assets
Cash and cash equivalents		0	0
Trading securities		3,418	3,013
Investment securities available-for-sale		660,676	633,892
Investment securities held-to-maturity		467,372	475,134
Loans, net		8,070	10,569
FDIC indemnification asset			0
Receivable from FDIC			678
Other earning assets	[1]	0	0
Gross asset value of derivatives		5,683	933
Total financial assets		1,145,219	1,124,219
Financial Liabilities
Non-contractual deposits		4,275,827	4,112,892
Contractual deposits		1,664,359	1,735,587
Federal Home Loan Bank advances		401,077	461,128
Short-term borrowings		16,201	12,410
Subordinated debentures		0	0
Gross liability value of derivatives		3	110
Total financial liabilities		6,357,467	6,322,127
Significant Unobservable Inputs (Level 3)
Financial Assets
Cash and cash equivalents		0	0
Trading securities		0	0
Investment securities available-for-sale		3,249	3,437
Investment securities held-to-maturity		0	0
Loans, net		5,701,104	5,625,949
FDIC indemnification asset			6,725
Receivable from FDIC			0
Other earning assets	[1]	23,743	25,736
Gross asset value of derivatives		0	0
Total financial assets		5,728,096	5,661,847
Financial Liabilities
Non-contractual deposits		0	0
Contractual deposits		0	0
Federal Home Loan Bank advances		0	0
Short-term borrowings		0	0
Subordinated debentures		85,721	92,517
Gross liability value of derivatives		0	0
Total financial liabilities		85,721	92,517
Carrying Value
Financial Assets
Cash and cash equivalents		182,020	144,696
Trading securities		3,418	3,013
Investment securities available-for-sale		663,925	637,329
Investment securities held-to-maturity		460,483	472,505
Loans, net		5,589,694	5,587,682
FDIC indemnification asset			6,725
Receivable from FDIC			678
Other earning assets	[1]	23,743	25,736
Gross asset value of derivatives		5,683	933
Total financial assets		6,928,966	6,879,297
Financial Liabilities
Non-contractual deposits		4,275,827	4,112,892
Contractual deposits		1,663,906	1,747,318
Federal Home Loan Bank advances		400,849	460,898
Short-term borrowings		16,200	12,410
Subordinated debentures		86,328	85,777
Gross liability value of derivatives		3	110
Total financial liabilities		6,443,113	6,419,405
Estimated Fair Value
Financial Assets
Cash and cash equivalents		182,020	144,696
Trading securities		3,418	3,013
Investment securities available-for-sale		663,925	637,329
Investment securities held-to-maturity		467,372	475,134
Loans, net		5,709,174	5,636,518
FDIC indemnification asset			6,725
Receivable from FDIC			678
Other earning assets	[1]	23,743	25,736
Gross asset value of derivatives		5,683	933
Total financial assets		7,055,335	6,930,762
Financial Liabilities
Non-contractual deposits		4,275,827	4,112,892
Contractual deposits		1,664,359	1,735,587
Federal Home Loan Bank advances		401,077	461,128
Short-term borrowings		16,201	12,410
Subordinated debentures		85,721	92,517
Gross liability value of derivatives		3	110
Total financial liabilities		$ 6,443,188	$ 6,414,644

[1] Includes Federal Home Loan Bank stock.