Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Amount
Tax at statutory rate	$ 26,268	$ 12,707	$ 47,219	$ 24,384
Changes resulting from:
Tax-exempt interest income	(1,832)	(1,139)	(3,589)	(2,278)
State taxes, net of federal benefit	258	0	470	0
Change in valuation allowance	38	0	49	0
Bank-owned life insurance adjustments	(335)	(287)	(679)	(355)
Income tax credits, net	(1,102)	(834)	(1,797)	(1,631)
Tax benefits in excess of compensation costs on share-based payments	(248)	(68)	(6,382)	(411)
Other, net	(11)	153	2	580
Income tax expense	$ 23,036	$ 10,532	$ 35,293	$ 20,289
Rate
Tax at statutory rate	35.00%	35.00%	35.00%	35.00%
Changes resulting from:
Tax-exempt interest income	(2.40%)	(3.10%)	(2.70%)	(3.30%)
State taxes, net of federal benefit	0.30%	0.00%	0.40%	0.00%
Change in valuation allowance	0.00%	0.00%	0.00%	0.00%
Bank-owned life insurance adjustments	(0.40%)	(0.80%)	(0.50%)	(0.50%)
Income tax credits, net	(1.50%)	(2.30%)	(1.30%)	(2.30%)
Tax benefits in excess of compensation costs on share-based payments	(0.30%)	(0.20%)	(4.70%)	(0.60%)
Other, net	0.00%	0.40%	0.00%	0.80%
Effective federal income tax rate	30.70%	29.00%	26.20%	29.10%