Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of provision for income taxes
Current income tax expense	$ 106,155	$ 87,064	$ 89,005
Deferred income tax benefit	(14,584)	(3,305)	(5,002)
Income tax expense	91,571	83,759	84,003
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	93,187	87,943	86,315
Tax-exempt interest	(2,285)	(2,589)	(2,345)
Other, net	669	(1,595)	33
Income tax expense	$ 91,571	$ 83,759	$ 84,003