Fair Value Measurements (Details 3) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
ASSETS
Held-to-maturity Securities	$ 448,139	$ 375,453
Held to Maturity, Fair Value, Total	455,776	379,699
Loans, net of allowance for loan losses(b)	5,442,916	4,915,633
LIABILITIES
Federal Home Loan Bank borrowings(c)	104,133	70,080
Customer Repurchase Agreements and other short-term borrowings	138,449	147,890
Wholesale Repurchase Agreements	0	50,000
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	73,520	73,685
Subordinated Debt	35,000	65,000
Time certificates of deposits(c)
LIABILITIES
Time certificates of deposits(c)	711,263	649,620
Accrued Liabilities, Fair Value Disclosure	713,473	651,180
Federal Home Loan Bank borrowings(c)
LIABILITIES
Federal Home Loan Bank borrowings(c)	104,133	70,080
Accrued Liabilities, Fair Value Disclosure	104,989	70,208
Customer repurchase agreements and other short-term borrowings(c)
LIABILITIES
Customer Repurchase Agreements and other short-term borrowings	138,449	147,890
Accrued Liabilities, Fair Value Disclosure	138,449	147,890
Wholesale repurchase agreements(c)
LIABILITIES
Wholesale Repurchase Agreements		50,000
Accrued Liabilities, Fair Value Disclosure		50,510
Junior subordinated debentures(d)
LIABILITIES
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	73,520	73,685
Accrued Liabilities, Fair Value Disclosure	70,925	70,045
Subordinated debentures(c)
LIABILITIES
Subordinated Debt	35,000	65,000
Accrued Liabilities, Fair Value Disclosure	35,282	64,198
Significant Other Observable Inputs (Level 2) | Time certificates of deposits(c)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	713,473	651,180
Significant Other Observable Inputs (Level 2) | Federal Home Loan Bank borrowings(c)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	104,989	70,208
Significant Other Observable Inputs (Level 2) | Junior subordinated debentures(d)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	70,925	70,045
Significant Unobservable Inputs (Level 3) | Customer repurchase agreements and other short-term borrowings(c)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	138,449	147,890
Significant Unobservable Inputs (Level 3) | Wholesale repurchase agreements(c)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure		50,510
Significant Unobservable Inputs (Level 3) | Subordinated debentures(c)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	35,282	64,198
U.S. Treasury securities
ASSETS
Held-to-maturity Securities	1,009	1,010
Held to Maturity, Fair Value, Total	1,084	1,073
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	1,084	1,073
Agency mortgage-backed securities
ASSETS
Held-to-maturity Securities	172,684	159,522
Held to Maturity, Fair Value, Total	178,402	164,944
Agency mortgage-backed securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	178,402	164,944
Agency collateralized mortgage obligations
ASSETS
Held-to-maturity Securities	230,820	198,220
Held to Maturity, Fair Value, Total	231,910	196,584
Agency collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	231,910	196,584
State, county, and municipal securities
ASSETS
Held-to-maturity Securities	225	424
Held to Maturity, Fair Value, Total	229	428
State, county, and municipal securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	229	428
Single issuer trust preferred securities issued by banks
ASSETS
Held-to-maturity Securities	1,500	1,500
Held to Maturity, Fair Value, Total	1,496	1,477
Single issuer trust preferred securities issued by banks | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	1,496	1,477
Small Business Administration Pooled Securities [Member]
ASSETS
Held-to-maturity Securities	36,901	9,775
Held to Maturity, Fair Value, Total	37,613	10,074
Small Business Administration Pooled Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
ASSETS
Held to Maturity, Fair Value, Total	0	0
Small Business Administration Pooled Securities [Member] | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	37,613	10,074
Small Business Administration Pooled Securities [Member] | Significant Unobservable Inputs (Level 3)
ASSETS
Held to Maturity, Fair Value, Total	0	0
Corporate debt securities
ASSETS
Held-to-maturity Securities	5,000	5,002
Held to Maturity, Fair Value, Total	5,042	5,119
Corporate debt securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	5,042	5,119
Loans, net of allowance for loan losses(b)
ASSETS
Loans, net of allowance for loan losses(b)		4,907,437
Loans Receivable, Fair Value Disclosure	5,406,492	4,875,283
Loans, net of allowance for loan losses(b) | Significant Unobservable Inputs (Level 3)
ASSETS
Loans Receivable, Fair Value Disclosure	$ 5,406,492	$ 4,875,283