Fair Value Measurements (Details 3) - USD ($) $ in Thousands		Jun. 30, 2019		Dec. 31, 2018
ASSETS
Debt Securities, Held-to-maturity		$ 797,359		$ 611,490
Held to Maturity, Fair Value, Total		808,656		603,640
Loans, net of allowance for loan losses(b)		8,884,827		6,841,901
Federal Home Loan Bank Stock		26,085		15,683
Bank Owned Life Insurance		197,292		160,456
LIABILITIES
Federal Home Loan Bank borrowings(f)		277,671		147,806
Long-term Debt		74,879	[1]	0
Long-term Debt, Fair Value	[1]	72,426
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust		62,847		76,173
Subordinated Debt		84,305		34,728
Deposits [Member]
LIABILITIES
Time certificates of deposits(f)	[2]	7,862,856		6,716,017
Accrued Liabilities, Fair Value Disclosure	[2]	7,862,856		6,716,017
Time certificates of deposits(f)
LIABILITIES
Time certificates of deposits(f)	[1]	1,445,059		711,103
Accrued Liabilities, Fair Value Disclosure	[1]	1,441,990		703,728
Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank borrowings(f)	[1]	277,671		147,806
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[1]	277,554		147,603
Junior subordinated debentures(g)
LIABILITIES
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	[3]	62,847		76,173
Accrued Liabilities, Fair Value Disclosure	[3]	64,586		73,827
Subordinated debentures(f)
LIABILITIES
Subordinated Debt	[1]	84,305		34,728
Accrued Liabilities, Fair Value Disclosure	[1]	87,963		32,509
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	0
Significant Other Observable Inputs (Level 2) | Deposits [Member]
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[2]	7,862,856		6,716,017
Significant Other Observable Inputs (Level 2) | Time certificates of deposits(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[1]	1,441,990		703,728
Significant Other Observable Inputs (Level 2) | Federal Home Loan Bank borrowings(f)
LIABILITIES
Federal Home Loan Bank Borrowings, Fair Value Disclosure	[1]	277,554
Accrued Liabilities, Fair Value Disclosure	[1]			147,603
Significant Other Observable Inputs (Level 2) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	72,426
Significant Other Observable Inputs (Level 2) | Junior subordinated debentures(g)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[3]	64,586		73,827
Significant Unobservable Inputs (Level 3) | Long-term Debt [Member]
LIABILITIES
Long-term Debt, Fair Value	[1]	0
Significant Unobservable Inputs (Level 3) | Subordinated debentures(f)
LIABILITIES
Accrued Liabilities, Fair Value Disclosure	[1]	87,963		32,509
U.S. Government agency securities
ASSETS
Debt Securities, Held-to-maturity	[4]	12,833
Held to Maturity, Fair Value, Total	[4]	12,963
U.S. Government agency securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	12,963
U.S. Treasury securities
ASSETS
Debt Securities, Held-to-maturity	[4]	1,003		1,004
Held to Maturity, Fair Value, Total	[4]	1,024		1,015
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	1,024		1,015
Agency mortgage-backed securities
ASSETS
Debt Securities, Held-to-maturity	[4]	423,825		252,484
Held to Maturity, Fair Value, Total	[4]	431,267		250,928
Agency mortgage-backed securities | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	431,267		250,928
Agency collateralized mortgage obligations
ASSETS
Debt Securities, Held-to-maturity	[4]	324,441		332,775
Held to Maturity, Fair Value, Total	[4]	327,718		326,724
Agency collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
ASSETS
Held to Maturity, Fair Value, Total	[4]	327,718		326,724
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]	33,757		23,727
Held to Maturity, Fair Value, Total	[4]	34,194		23,483
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]	34,194		23,483
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]	8,858,356		6,812,792
Loans Receivable, Fair Value Disclosure	[5]	8,719,439		6,635,209
Loans, net of allowance for loan losses(b) | Significant Unobservable Inputs (Level 3)
ASSETS
Loans Receivable, Fair Value Disclosure	[5]	8,719,439		6,635,209
Investment in Federal Home Loan Bank Stock [Member]
ASSETS
Federal Home Loan Bank Stock	[6]	26,085		15,683
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	[6]	26,085		15,683
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]	26,085		15,683
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]	197,292		160,456
Bank Owned Life Insurance	[7]	197,292		160,456
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]	197,292		160,456
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.