Income Taxes (Effective Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount
Tax at statutory rate													$ 68,443	$ 89,706	$ 52,548
Tax-exempt interest income													(6,513)	(9,001)	(5,320)
State taxes, net of federal benefit													434	369	13
Change in valuation allowance													317	(1,089)	(706)
Bank-owned life insurance adjustments													(838)	(1,696)	(832)
Director plan change in control													0	0	(508)
Income tax credits, net													(16,148)	(11,449)	(2,454)
Nondeductible transaction expenses														156	2,100
Tax benefits in excess of compensation costs on share-based payments													(1,782)	(5,886)	(2,240)
Impact of Tax Cuts and Jobs Act													(2,939)	46,660	0
Other, net													(168)	(990)	(495)
Income tax provision	$ 5,200	$ 11,312	$ 12,434	$ 12,955	$ 61,234	$ 10,253	$ 23,036	$ 12,257	$ 18,969	$ 2,848	$ 10,532	$ 9,757	$ 41,901	$ 106,780	$ 42,106
Effective Income Tax Rate, Tax Rate Reconciliation, Percent
Tax at statutory rate													21.00%	35.00%	35.00%
Tax-exempt interest income													(2.00%)	(3.50%)	(3.50%)
State taxes, net of federal benefit													0.10%	0.10%	0.00%
Change in valuation allowance													0.10%	(0.40%)	(0.50%)
Bank-owned life insurance adjustments													(0.20%)	(0.70%)	(0.60%)
Director plan change in control													0.00%	0.00%	(0.30%)
Income tax credits, net													(4.90%)	(4.40%)	(1.60%)
Nondeductible transaction expenses													0.00%	0.10%	1.40%
Tax benefits in excess of compensation costs on share-based payments													(0.50%)	(2.30%)	(1.50%)
Impact of Tax Cuts and Jobs Act													(0.90%)	18.20%	0.00%
Other, net													(0.10%)	(0.40%)	(0.40%)
Income tax expense													12.90%	41.70%	28.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, FDIC Insurance Premiums, Amount													$ 1,095	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Nondeductible Expense, FDIC Insurance Premiums, Percent													0.30%	0.00%	0.00%