Fair Value Measurements (Details 3) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Equity		$ 20,075	$ 0
ASSETS
Held-to-maturity Securities		528,861	497,688
Held to Maturity, Fair Value, Total		517,555	494,194
Loans, net of allowance for loan losses(b)		6,301,194	6,294,910
Federal Home Loan Bank Stock		13,027	11,597
Bank Owned Life Insurance		152,568	151,528
LIABILITIES
Federal Home Loan Bank borrowings(f)		53,257	53,264
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust		73,075	73,073
Subordinated Debt		34,693	34,682
Deposits [Member]
LIABILITIES
Time certificates of deposits(f)	[1]	6,096,756	6,084,952
Accrued Liabilities, Fair Value Disclosure	[1]	6,096,756	6,084,952
Time certificates of deposits(f)
LIABILITIES
Time certificates of deposits(f)	[2]	654,755	644,301
Accrued Liabilities, Fair Value Disclosure	[2]	646,819	639,060
Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank borrowings(f)	[2]	53,257	53,264
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[2]	52,176	52,111
Customer repurchase agreements and other short-term borrowings(f)
LIABILITIES
Customer repurchase agreements	[2]	137,914	162,679
Accrued Liabilities, Fair Value Disclosure	[2]	137,914	162,679
Junior subordinated debentures(g)
LIABILITIES
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	[3]	73,075	73,073
Accrued Liabilities, Fair Value Disclosure	[3]	72,283	74,680
Subordinated debentures(f)
LIABILITIES
Subordinated Debt	[2]	34,693	34,682
Accrued Liabilities, Fair Value Disclosure	[2]	32,429	32,707
Significant Other Observable Inputs (Level 2) | Deposits [Member]
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[1]	6,096,756	6,084,952
Significant Other Observable Inputs (Level 2) | Time certificates of deposits(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[2]	646,819	639,060
Significant Other Observable Inputs (Level 2) | Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[2]	52,176
Accrued Liabilities, Fair Value Disclosure	[2]		52,111
Significant Other Observable Inputs (Level 2) | Junior subordinated debentures(g)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[3]	72,283	74,680
Significant Unobservable Inputs (Level 3) | Customer repurchase agreements and other short-term borrowings(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[2]	137,914	162,679
Significant Unobservable Inputs (Level 3) | Subordinated debentures(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[2]	32,429	32,707
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Equity		20,075
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Equity		20,075
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Equity		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Equity		0
U.S. Treasury securities
ASSETS
Held-to-maturity Securities	[4]	1,005	1,006
Held to Maturity, Fair Value, Total	[4]	1,021	1,035
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	1,021	1,035
Agency mortgage-backed securities
ASSETS
Held-to-maturity Securities	[4]	192,961	204,768
Held to Maturity, Fair Value, Total	[4]	190,409	205,823
Agency mortgage-backed securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	190,409	205,823
Agency collateralized mortgage obligations
ASSETS
Held-to-maturity Securities	[4]	306,395	262,998
Held to Maturity, Fair Value, Total	[4]	297,818	258,408
Agency collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	297,818	258,408
Single issuer trust preferred securities issued by banks
ASSETS
Held-to-maturity Securities	[4]	1,500	1,500
Held to Maturity, Fair Value, Total	[4]	1,521	1,529
Single issuer trust preferred securities issued by banks | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	1,521	1,529
Small Business Administration Pooled Securities [Member]
ASSETS
Held-to-maturity Securities	[4]	27,000	27,416
Held to Maturity, Fair Value, Total	[4]	26,786	27,399
Small Business Administration Pooled Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
ASSETS
Held to Maturity, Fair Value, Total	[4]	0	0
Small Business Administration Pooled Securities [Member] | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	26,786	27,399
Small Business Administration Pooled Securities [Member] | Significant Unobservable Inputs (Level 3)
ASSETS
Held to Maturity, Fair Value, Total	[4]	0	0
Loans, net of allowance for loan losses(b)
ASSETS
Loans, net of allowance for loan losses(b)	[5]	6,269,081	6,261,343
Loans Receivable, Fair Value Disclosure	[5]	6,103,312	6,116,051
Loans, net of allowance for loan losses(b) | Significant Unobservable Inputs (Level 3)
ASSETS
Loans Receivable, Fair Value Disclosure	[5]	6,103,312	6,116,051
Investment in Federal Home Loan Bank Stock [Member]
ASSETS
Federal Home Loan Bank Stock	[6]	13,027	11,597
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	13,027	11,597
Investment in Federal Home Loan Bank Stock [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
ASSETS
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	0	0
Investment in Federal Home Loan Bank Stock [Member] | Significant Other Observable Inputs (Level 2)
ASSETS
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	13,027	11,597
Investment in Federal Home Loan Bank Stock [Member] | Significant Unobservable Inputs (Level 3)
ASSETS
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	0	0
Cash Surrender Value [Member]
ASSETS
Cash Surrender Value, Fair Value Disclosure	[7]	152,568	151,528
Bank Owned Life Insurance	[7]	152,568	151,528
Cash Surrender Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
ASSETS
Cash Surrender Value, Fair Value Disclosure	[7]	0	0
Cash Surrender Value [Member] | Significant Other Observable Inputs (Level 2)
ASSETS
Cash Surrender Value, Fair Value Disclosure	[7]	152,568	151,528
Cash Surrender Value [Member] | Significant Unobservable Inputs (Level 3)
ASSETS
Cash Surrender Value, Fair Value Disclosure	[7]	$ 0	$ 0

[1] Fair value of demand deposits, savings and interest checking accounts and money market deposits is the amount payable on demand at the reporting date.

[2] Fair value was determined by discounting anticipated future cash payments using rates currently available for instruments with similar remaining maturities.

[3] Fair value was determined based upon market prices of securities with similar terms and maturities.

[4] The fair values presented are based on quoted market prices, where available. If quoted market prices are not available, fair values are based on quoted market prices of comparable instruments and/or discounted cash flow analysis.

[5] estimated solely by discounting the future cash flows using the current rates at which similar loans would be made to borrowers with similar credit ratings and for the same remaining maturities or cash flows. Additionally, this amount excludes collateral dependent impaired loans, which are deemed to be marked to fair value on a nonrecurring basis.

[6] FHLB stock has no quoted market value and is carried at cost, therefore the carrying amount approximates fair value.

[7] Cash surrender value of life insurance is recorded at its cash surrender value (or the amount that can be realized upon surrender of the policy), therefore carrying amount approximates fair value.