Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal									$ 28,380	$ 31,679	$ 17,004
State									1,354	2,131	995
Total									29,734	33,810	17,999
Deferred
Federal									22,314	10,480	12,625
State									1,147	557	1,126
Revaluation of net deferred tax assets as a result of the Tax Cuts and Jobs Act									14,486	0	0
Total									37,947	11,037	13,751
Total income tax expense	$ 30,234	$ 14,199	$ 11,993	$ 11,255	$ 11,461	$ 11,706	$ 11,154	$ 10,526	$ 67,681	$ 44,847	$ 31,750