Segment Reporting - Revenues by Geographic Location (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
Segment Reporting Information [Line Items]
Total revenues	$ 33,914	$ 33,492	$ 33,756	$ 32,623	$ 31,092	$ 31,777	$ 31,023	$ 29,129	$ 133,785	$ 123,021	$ 130,936
U.S.
Segment Reporting Information [Line Items]
Total revenues									111,097	103,261	109,816
Canada
Segment Reporting Information [Line Items]
Total revenues									9,169	7,714	9,238
Europe
Segment Reporting Information [Line Items]
Total revenues									3,873	5,416	6,019
Asia
Segment Reporting Information [Line Items]
Total revenues									6,312	4,872	4,538
Australia
Segment Reporting Information [Line Items]
Total revenues									$ 3,334	$ 1,758	$ 1,325