Quarterly Results of Operations (unaudited) - Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Results of Operations (unaudited)
Revenue	$ 69,358	$ 65,650	$ 64,451	$ 67,521	$ 70,458	$ 79,317	$ 78,437	$ 73,283	$ 266,980	$ 301,495	$ 203,051
Gross profit	26,947	24,104	25,131	23,415	21,973	29,179	27,174	23,380	99,598	101,706	70,164
Net income	$ 3,965	$ 2,151	$ 2,937	$ 1,948	$ 826	$ 6,101	$ 5,883	$ 1,868	$ 11,001	$ 14,678	$ (11,266)
Net income per basic share (in dollars per share)	$ 0.13	$ 0.07	$ 0.10	$ 0.07	$ 0.03	$ 0.21	$ 0.21	$ 0.07	$ 0.38	$ 0.51	$ (0.40)
Net income per diluted share (in dollars per share)	$ 0.13	$ 0.07	$ 0.10	$ 0.06	$ 0.03	$ 0.20	$ 0.20	$ 0.06	$ 0.36	$ 0.49	$ (0.40)