Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets
Interest-earning deposits with banks	$ 612,883	$ 434,867
Debt securities available for sale at fair value	4,190,066	5,210,134
Debt Securities, Held-to-Maturity, Amortized Cost	2,024,715	0
Debt Securities, Held-to-maturity, Fair Value	2,032,980	0
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	218,649	218,899
Interest-earning deposits with banks	612,883	434,867
Debt securities available for sale at fair value	4,190,066	5,210,134
Debt Securities, Held-to-maturity, Fair Value	2,032,980
FHLB stock	10,280	10,280
Loans held for sale	13,179	26,481
Loans	9,955,668	9,720,592
Liabilities
Deposits	326,735	338,815
FHLB advances	8,878	9,295
Repurchase agreements	70,994	73,859
Subordinated Debentures	35,171	35,414
Carrying Amount
Assets
Cash and due from banks	218,649	218,899
Interest-earning deposits with banks	612,883	434,867
Debt securities available for sale at fair value	4,190,066	5,210,134
Debt Securities, Held-to-Maturity, Amortized Cost	2,024,715
FHLB stock	10,280	10,280
Loans held for sale	13,179	26,481
Loans	9,550,128	9,278,520
Liabilities
Deposits	327,882	338,845
FHLB advances	7,386	7,414
Repurchase agreements	70,994	73,859
Subordinated Debentures	35,000	35,092
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	218,649	218,899
Interest-earning deposits with banks	612,883	434,867
Debt securities available for sale at fair value	0	0
Debt Securities, Held-to-maturity, Fair Value	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	0	0
Liabilities
Deposits	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Subordinated Debentures	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Debt securities available for sale at fair value	4,190,066	5,210,134
Debt Securities, Held-to-maturity, Fair Value	2,032,980
FHLB stock	10,280	10,280
Loans held for sale	13,179	26,481
Loans	0	0
Liabilities
Deposits	326,735	338,815
FHLB advances	8,878	9,295
Repurchase agreements	70,994	73,859
Subordinated Debentures	35,171	35,414
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Debt securities available for sale at fair value	0	0
Debt Securities, Held-to-maturity, Fair Value	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	9,955,668	9,720,592
Liabilities
Deposits	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Subordinated Debentures	0	0
Interest Rate Swap Contracts | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	32,546	46,184
Liabilities
Interest rate derivative liability	32,853	46,637
Interest Rate Swap Contracts | Carrying Amount
Assets
Interest rate derivative asset	32,546	46,184
Liabilities
Interest rate derivative liability	32,853	46,637
Interest Rate Swap Contracts | Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	0	0
Liabilities
Interest rate derivative liability	0	0
Interest Rate Swap Contracts | Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	32,546	46,184
Liabilities
Interest rate derivative liability	32,853	46,637
Interest Rate Swap Contracts | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	0	0
Liabilities
Interest rate derivative liability	0	0
Interest Rate Lock Commitments Contracts | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	585	1,096
Interest Rate Lock Commitments Contracts | Carrying Amount
Assets
Interest rate derivative asset	585	1,096
Interest Rate Lock Commitments Contracts | Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	0	0
Interest Rate Lock Commitments Contracts | Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	0	0
Interest Rate Lock Commitments Contracts | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Interest rate derivative asset	585	1,096
Interest rate Forward Sales Contracts | Estimate of Fair Value Measurement [Member]
Liabilities
Interest rate derivative liability	23	165
Interest rate Forward Sales Contracts | Carrying Amount
Liabilities
Interest rate derivative liability	23	165
Interest rate Forward Sales Contracts | Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Liabilities
Interest rate derivative liability	0	0
Interest rate Forward Sales Contracts | Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Liabilities
Interest rate derivative liability	23	165
Interest rate Forward Sales Contracts | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Liabilities
Interest rate derivative liability	$ 0	$ 0