Federal and State Income Taxes Federal and State Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	$ 44,880	$ 37,474	$ 137,048	$ 93,189
Tax exempt revenue	(3,001)	(2,391)	(9,336)	(7,491)
Effect of state income taxes, net of federal benefit	2,486	1,364	7,875	5,222
Utilization of tax credits:
Low-income housing tax credit, net of amortization	(23)	(623)	(2,272)	(2,505)
Other tax credits	(364)	(522)	(1,091)	(1,564)
Bank-owned life insurance	(705)	(813)	(2,252)	(2,414)
Share-based compensation	(169)	0	(2,470)	0
Other, net	(666)	(2,533)	744	(556)
Total income tax expense	$ 42,438	$ 31,956	$ 128,246	$ 83,881
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Tax exempt revenue (in hundredths)	(2.30%)	(2.20%)	(2.40%)	(2.80%)
Effect of state income taxes, net of federal benefit (in hundredths)	1.90%	1.30%	2.00%	2.00%
Utilization of tax credits: [Abstract]
Low-income housing tax credit, net of amortization (in hundredths)	(0.00%)	(0.60%)	(0.60%)	(0.90%)
Other tax credits (in hundredths)	(0.30%)	(0.50%)	(0.30%)	(0.60%)
Bank-owned life insurance	0.50%	0.80%	0.60%	0.90%
Share-based compensation (in hundredths)	(0.10%)	0.00%	(0.60%)	0.00%
Other, net (in hundredths)	(0.60%)	(2.40%)	0.30%	(0.30%)
Total (in hundredths)	33.10%	29.80%	32.80%	31.50%