Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense at federal statutory rate									$ 58,795	$ 102,205	$ 92,743
SALT expense, net of federal									7,884	14,782	11,354
Tax-exempt interest income, net									(7,181)	(6,752)	(6,475)
Increase in cash surrender value of life insurance									(3,058)	(3,069)	(3,069)
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount									(484)	2,251	4,483
Non-deductible FDIC deposit insurance premiums									2,172	1,904	2,215
Tax Act impacts, net									0	0	10,982
Other, net									(257)	2,850	88
Income tax expense	$ 15,118	$ 18,289	$ 14,802	$ 11,144	$ 25,966	$ 25,411	$ 26,451	$ 26,141	$ 59,353	$ 103,969	$ 81,215
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax expense at federal statutory rate									21.00%	21.00%	21.00%
SALT expense, net of federal									2.80%	3.00%	2.60%
Tax-exempt interest income, net									(2.60%)	(1.40%)	(1.50%)
Increase in cash surrender value of life insurance									(1.10%)	(0.60%)	(0.70%)
Tax deficiencies (excess tax benefits), net									(0.20%)	0.40%	1.00%
Non-deductible FDIC deposit insurance premiums									0.80%	0.40%	0.50%
Tax Act impacts, net									0.00%	0.00%	2.50%
Other, net									(0.10%)	0.60%	0.00%
Income tax expense and effective tax rate									21.20%	21.40%	18.40%