Other Data (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State income tax expense:
Texas gross margins tax	$ 608	$ 562	$ 528
Other	0	2	37
Total state income tax expense	608	564	565
State income tax payments, net of refunds and collections	$ 555	$ 544	758
Income tax expense in discontinued operations			$ 50