Income Taxes, Current and Deferred Amounts of Income Tax Expense Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 76,525	$ 73,781	$ 82,449
State	11,576	2,885	2,560
Total current	88,101	76,666	85,009
Deferred:
Federal	19,755	3,338	(10,606)
State	1,647	7,318	7,084
Total deferred	21,402	10,656	(3,522)
Total income tax expense	$ 109,503	$ 87,322	$ 81,487