Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of provision for income taxes
Current income tax expense	$ 109,727	$ 106,155	$ 87,064
Deferred income tax benefit	(2)	(14,584)	(3,305)
Income tax expense	109,725	91,571	83,759
Reconciliation of the provision for income taxes, with amounts determined by applying the statutory federal income tax rates to pre-tax income
Income tax at statutory rate	112,032	93,187	87,943
Tax-exempt interest	(2,270)	(2,285)	(2,589)
Other, net	(37)	669	(1,595)
Income tax expense	$ 109,725	$ 91,571	$ 83,759