Income Taxes (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Taxes computed at statutory rate, amount	$ 80,244	$ 107,952	$ 65,423
State income taxes, net of federal income tax benefit, amount	8,770	4,288	2,104
Tax-exempt interest, amount	(10,803)	(18,870)	(14,497)
Bank owned life insurance contracts, amount	(2,019)	(5,360)	(4,833)
Tax credits, amount	(11,344)	(9,286)	(10,410)
Employee share-based compensation, amount	(1,380)	(5,824)
FDIC assessment disallowance, amount	2,818
Return to provision adjustment, amount	(9,942)	(120)	(549)
Impact of deferred tax asset re-measurement		19,520
Other, net, amount	2,002	502	389
Total included in net income	$ 58,346	$ 92,802	$ 37,627
Taxes computed at statutory rate	21.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	2.30%	1.40%	1.10%
Tax-exempt interest	(2.80%)	(6.10%)	(7.80%)
Bank owned life insurance	(0.50%)	(1.70%)	(2.60%)
Tax credits	(3.00%)	(3.10%)	(5.60%)
Employee share-based compensation	(0.30%)	(1.90%)
FDIC assessment disallowance	0.70%
Return to provision adjustment	(2.60%)		(0.30%)
Impact of deferred tax asset re-measurement		6.30%
Other, net	0.50%	0.20%	0.30%
Income tax expense	15.30%	30.10%	20.10%