Income Taxes, Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current taxes [Abstract]
Federal	$ 771	$ (426)	$ 457
State	373	311	670
Deferred taxes [Abstract]
Federal	37,565	18,910	23,342
State	4,844	3,178	4,816
Income tax expense	$ 43,553	$ 21,973	$ 29,285