Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets
Interest-earning deposits with banks	$ 880,232		$ 24,132
Debt securities available for sale at fair value	3,693,787		3,746,142
Equity Securities	13,425	$ 0	0	$ 0	$ 0	$ 0
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	217,461		223,541
Interest-earning deposits with banks	880,232		24,132
Debt securities available for sale at fair value	3,693,787		3,746,142
Equity Securities	13,425
FHLB stock	16,280		48,120
Loans held for sale	28,803		17,718
Loans	10,061,835		8,883,865
Interest rate contracts	54,424		19,144
Interest Rate Cash Flow Hedge Asset at Fair Value	38,421		14,727
Liabilities
Deposits	340,419		397,736
FHLB advances and FRB borrowings	159,400
FHLB advances			952,762
Repurchase agreements	51,479		64,437
Subordinated Debt Obligations, Fair Value Disclosure	35,227		35,491
Interest rate contracts	54,898		19,145
Reported Value Measurement [Member]
Assets
Cash and due from banks	217,461		223,541
Interest-earning deposits with banks	880,232		24,132
Debt securities available for sale at fair value	3,693,787		3,746,142
Equity Securities	13,425
FHLB stock	16,280		48,120
Loans held for sale	28,803		17,718
Loans	9,620,352		8,659,497
Interest rate contracts	54,424		19,144
Interest Rate Cash Flow Hedge Asset at Fair Value	38,421		14,727
Liabilities
Deposits	340,192		400,070
FHLB advances and FRB borrowings	157,441
FHLB advances			953,469
Repurchase agreements	51,479		64,437
Subordinated Debt Obligations, Fair Value Disclosure	35,185		35,277
Interest rate contracts	54,898		19,145
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	217,461		223,541
Interest-earning deposits with banks	880,232		24,132
Debt securities available for sale at fair value	0		0
Equity Securities	0
FHLB stock	0		0
Loans held for sale	0		0
Loans	0		0
Interest rate contracts	0		0
Interest Rate Cash Flow Hedge Asset at Fair Value	0		0
Liabilities
Deposits	0		0
FHLB advances and FRB borrowings	0
FHLB advances			0
Repurchase agreements	0		0
Subordinated Debt Obligations, Fair Value Disclosure	0		0
Interest rate contracts	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	3,693,787		3,746,142
Equity Securities	0
FHLB stock	16,280		48,120
Loans held for sale	28,803		17,718
Loans	0		0
Interest rate contracts	54,424		19,144
Interest Rate Cash Flow Hedge Asset at Fair Value	38,421		14,727
Liabilities
Deposits	340,419		397,736
FHLB advances and FRB borrowings	159,400
FHLB advances			952,762
Repurchase agreements	51,479		64,437
Subordinated Debt Obligations, Fair Value Disclosure	35,227		35,491
Interest rate contracts	54,898		19,145
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
Equity Securities	13,425
FHLB stock	0		0
Loans held for sale	0		0
Loans	10,061,835		8,883,865
Interest rate contracts	0		0
Interest Rate Cash Flow Hedge Asset at Fair Value	0		0
Liabilities
Deposits	0		0
FHLB advances and FRB borrowings	0
FHLB advances			0
Repurchase agreements	0		0
Subordinated Debt Obligations, Fair Value Disclosure	0		0
Interest rate contracts	$ 0		$ 0