Fair Value Measurements (Details 3) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
ASSETS
Debt Securities, Held-to-maturity		$ 777,798	$ 740,806
Held to Maturity, Fair Value, Total		809,355	753,263
Loans, net of allowance for credit losses(b)		8,824,054	8,805,899
Federal Home Loan Bank Stock		23,274	14,424
Bank Owned Life Insurance		197,772	197,372
LIABILITIES
Federal Home Loan Bank borrowings(f)		358,591	115,748
Long-term Debt	[1]	74,920	74,906
Long-term Debt, Fair Value	[1]	73,572	72,219
Subordinated Debt		49,625	49,601
Deposits [Member]
LIABILITIES
Time certificates of deposits(f)	[2]	8,146,490	7,752,052
Accrued Liabilities, Fair Value Disclosure	[2]	8,146,490	7,752,052
Time certificates of deposits(f)
LIABILITIES
Time certificates of deposits(f)	[1]	1,269,708	1,395,315
Accrued Liabilities, Fair Value Disclosure	[1]	1,279,983	1,396,760
Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank borrowings(f)	[1]	358,591	115,748
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[1]	359,249	115,881
Junior subordinated debentures(g)
LIABILITIES
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	[3]	62,849	62,848
Accrued Liabilities, Fair Value Disclosure	[3]	61,528	65,603
Subordinated debentures(f)
LIABILITIES
Subordinated Debt	[1]	49,625	49,601
Accrued Liabilities, Fair Value Disclosure	[1]	51,896	52,870
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	0	0
Significant Other Observable Inputs (Level 2) | Deposits [Member]
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[2]	8,146,490	7,752,052
Significant Other Observable Inputs (Level 2) | Time certificates of deposits(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[1]	1,279,983	1,396,760
Significant Other Observable Inputs (Level 2) | Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[1]	359,249
Accrued Liabilities, Fair Value Disclosure	[1]		115,881
Significant Other Observable Inputs (Level 2) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	73,572	72,219
Significant Other Observable Inputs (Level 2) | Junior subordinated debentures(g)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[3]	61,528	65,603
Significant Unobservable Inputs (Level 3) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	0	0
Significant Unobservable Inputs (Level 3) | Subordinated debentures(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[1]	51,896	52,870
U.S. Government agency securities
ASSETS
Debt Securities, Held-to-maturity	[4]		12,874
Held to Maturity, Fair Value, Total	[4]		12,997
U.S. Government agency securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]		12,997
U.S. Treasury securities
ASSETS
Debt Securities, Held-to-maturity	[4]	4,029	4,032
Held to Maturity, Fair Value, Total	[4]	4,139	4,053
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	4,139	4,053
Agency mortgage-backed securities
ASSETS
Debt Securities, Held-to-maturity	[4]	463,632	397,414
Held to Maturity, Fair Value, Total	[4]	482,363	405,802
Agency mortgage-backed securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	482,363	405,802
Agency collateralized mortgage obligations
ASSETS
Debt Securities, Held-to-maturity	[4]	277,921	293,662
Held to Maturity, Fair Value, Total	[4]	289,902	297,314
Agency collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	289,902	297,314
Single issuer trust preferred securities issued by banks
ASSETS
Debt Securities, Held-to-maturity	[4]	1,500	1,500
Held to Maturity, Fair Value, Total	[4]	1,490	1,490
Single issuer trust preferred securities issued by banks | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	1,490	1,490
Small Business Administration Pooled Securities [Member]
ASSETS
Debt Securities, Held-to-maturity	[4]	30,716	31,324
Held to Maturity, Fair Value, Total	[4]	31,461	31,607
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]	31,461	31,607
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 credit losses(b)
ASSETS
Loans, net of allowance for credit losses(b)	[5]	8,784,610	8,780,384
Loans Receivable, Fair Value Disclosure	[5]	8,626,697	8,613,635
Loans, net of allowance for credit losses(b) | Significant Unobservable Inputs (Level 3)
ASSETS
Loans Receivable, Fair Value Disclosure	[5]	8,626,697	8,613,635
Investment in Federal Home Loan Bank Stock [Member]
ASSETS
Federal Home Loan Bank Stock	[6]	23,274	14,424
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	23,274	14,424
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]	23,274	14,424
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]	197,772	197,372
Bank Owned Life Insurance	[7]	197,772	197,372
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]	197,772	197,372
Cash Surrender Value [Member] | Significant Unobservable Inputs (Level 3)
ASSETS
Cash Surrender Value, Fair Value Disclosure	[7]	$ 0	$ 0

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

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

[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] Fair value of loans is measured using the exit price valuation method, determined primarily 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, while incorporating liquidity and credit assumptions. 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.