Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense at federal statutory rate									$ 102,205	$ 92,743	$ 123,826
SALT expense, net of federal									14,782	11,354	8,189
Tax-exempt interest income, net									(6,752)	(6,475)	(10,826)
Increase in cash surrender value of life insurance									(3,069)	(3,069)	(5,120)
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount									2,251	4,483	6,349
Non-deductible FDIC deposit insurance premiums									1,904	2,215	0
SALT DTA adjustments, net of federal									0	0	28,724
Tax Act impacts, net									0	10,982	(20,891)
Other, net									2,850	88	3,536
Income tax expense	$ 25,966	$ 25,411	$ 26,451	$ 26,141	$ 26,697	$ 13,700	$ 20,743	$ 20,075	$ 103,969	$ 81,215	$ 98,351
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax expense at federal statutory rate									21.00%	21.00%	35.00%
SALT expense, net of federal									3.00%	2.60%	2.30%
Tax-exempt interest income, net									(1.40%)	(1.50%)	(3.10%)
Increase in cash surrender value of life insurance									(0.60%)	(0.70%)	(1.40%)
Excess tax benefits, net									0.40%	1.00%	1.80%
Non-deductible FDIC deposit insurance premiums									0.40%	0.50%	0.00%
SALT DTA adjustments, net of federal									0.00%	0.00%	8.10%
Tax Act impacts, net									0.00%	2.50%	(5.90%)
Other, net									0.60%	0.00%	1.00%
Income tax expense and effective tax rate									21.40%	18.40%	27.80%