Federal and State Income Taxes Federal and State Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	$ 47,800	$ 33,869	$ 92,168	$ 55,715
Tax exempt revenue	(3,224)	(2,568)	(6,335)	(5,100)
Effect of state income taxes, net of federal benefit	2,944	1,557	5,389	3,858
Utilization of tax credits:
Low-income housing tax credit, net of amortization	(526)	(572)	(2,249)	(1,882)
Other tax credits	(363)	(521)	(727)	(1,042)
Bank-owned life insurance	(775)	(810)	(1,547)	(1,601)
Share-based compensation	1,636	0	(2,301)	0
Other, net	213	(458)	1,410	1,977
Total income tax expense	$ 47,705	$ 30,497	$ 85,808	$ 51,925
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)	(2.40%)	(2.70%)	(2.40%)	(3.20%)
Effect of state income taxes, net of federal benefit (in hundredths)	2.20%	1.60%	2.00%	2.40%
Utilization of tax credits: [Abstract]
Low-income housing tax credit, net of amortization (in hundredths)	(0.40%)	(0.60%)	(0.80%)	(1.20%)
Other tax credits (in hundredths)	(0.30%)	(0.50%)	(0.30%)	(0.60%)
Effective Income Tax Rate Reconciliation, Deduction, Other, Percent	0.60%	0.80%	0.60%	1.00%
Share-based compensation (in hundredths)	1.20%	0.00%	(0.90%)	0.00%
Other, net (in hundredths)	0.20%	(0.50%)	0.60%	1.20%
Total (in hundredths)	34.90%	31.50%	32.60%	32.60%