Business Segment, Geographic and Quarterly Financial Data - Operations by Geographic Area (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
Revenues:
Revenues	$ 13,386	$ 13,548	$ 9,741	$ 8,491	$ 9,568	$ 12,596	$ 15,175	$ 17,822	$ 45,166	$ 55,161	$ 73,664
Assets
Assets:	50,484				57,788				50,484	57,788
United States
Revenues:
Revenues									29,510	42,545	51,485
Assets
Assets:	29,945				37,684				29,945	37,684
Foreign
Revenues:
Revenues									15,656	12,616	$ 22,179
Assets
Assets:	$ 20,539				$ 20,104				$ 20,539	$ 20,104