Other Data (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
State income tax expense:
Texas gross margins tax	$ 586	$ 608	$ 562
Other	0	0	2
Total state income tax expense	586	608	564
State income tax payments, net of refunds and collections	$ 637	$ 555	$ 544