Business Segment, Geographic and Quarterly Financial Data - Operations by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Revenues	$ 15,827	$ 16,070	$ 11,847	$ 12,791	$ 13,386	$ 13,548	$ 9,741	$ 8,491	$ 56,535	$ 45,166	$ 55,161
Assets
Assets:	51,719				50,484				51,719	50,484
United States
Revenues:
Revenues									43,887	29,510	42,545
Assets
Assets:	36,784				29,945				36,784	29,945
Foreign
Revenues:
Revenues									12,648	15,656	$ 12,616
Assets
Assets:	$ 14,935				$ 20,539				$ 14,935	$ 20,539