Income Taxes (Effective Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount
Tax at statutory rate													$ 89,706	$ 52,548	$ 43,341
Tax-exempt interest income													(9,001)	(5,320)	(3,943)
State taxes, net of federal benefit													369	13	0
Change in valuation allowance													(1,089)	(706)	0
Bank-owned life insurance adjustments													(1,696)	(832)	(124)
Director plan change in control													0	(508)	0
Income tax credits, net													(11,449)	(2,454)	(2,557)
Nondeductible transaction expenses													156	2,100	411
Tax benefits in excess of compensation costs on share-based payments													(5,886)	(2,240)	0
Impact of Tax Cuts and Jobs Act													46,660	0	0
Other, net													(990)	(495)	(128)
Income tax provision	$ 61,234	$ 10,253	$ 23,036	$ 12,257	$ 18,969	$ 2,848	$ 10,532	$ 9,757	$ 10,200	$ 9,600	$ 9,100	$ 8,100	$ 106,780	$ 42,106	$ 37,000
Effective Income Tax Rate, Tax Rate Reconciliation, Percent
Tax at statutory rate													35.00%	35.00%	35.00%
Tax-exempt interest income													(3.50%)	(3.50%)	(3.20%)
State taxes, net of federal benefit													0.10%	0.00%	0.00%
Change in valuation allowance													(0.40%)	(0.50%)	0.00%
Bank-owned life insurance adjustments													(0.70%)	(0.60%)	(0.10%)
Director plan change in control													0.00%	(0.30%)	0.00%
Income tax credits, net													(4.40%)	(1.60%)	(2.10%)
Nondeductible transaction expenses													0.10%	1.40%	0.30%
Tax benefits in excess of compensation costs on share-based payments													(2.30%)	(1.50%)	(0.00%)
Impact of Tax Cuts and Jobs Act													18.20%	0.00%	0.00%
Other, net													(0.40%)	(0.40%)	0.00%
Income tax expense													41.70%	28.00%	29.90%