Income Taxes (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Taxes computed at statutory rate, amount	$ 82,475	$ 80,244	$ 107,952
State income taxes, net of federal income tax benefit, amount	7,204	8,770	4,288
Tax-exempt interest, amount	(10,435)	(10,803)	(18,870)
Life insurance contracts, amount	(3,901)	(2,019)	(5,360)
Tax credits, amount	(10,293)	(11,344)	(9,286)
Employee share-based compensation, amount	(842)	(1,380)	(5,824)
FDIC assessment disallowance, amount	1,895	2,818
Return to provision adjustment, amount	(1,459)	(9,942)	(120)
Impact of deferred tax asset re-measurement			19,520
Other, net, amount	715	2,002	502
Total included in net income	$ 65,359	$ 58,346	$ 92,802
Taxes computed at statutory rate	21.00%	21.00%	35.00%
State income taxes, net of federal income tax benefit	1.80%	2.30%	1.40%
Tax-exempt interest	(2.70%)	(2.80%)	(6.10%)
Life insurance contracts	(1.00%)	(0.50%)	(1.70%)
Tax credits	(2.60%)	(3.00%)	(3.10%)
Employee share-based compensation	(0.20%)	(0.30%)	(1.90%)
FDIC assessment disallowance	0.50%	0.70%
Return to provision adjustment	(0.40%)	(2.60%)
Impact of deferred tax asset re-measurement			6.30%
Other, net	0.20%	0.50%	0.20%
Income tax expense	16.60%	15.30%	30.10%