Summary of Significant Accounting Policies - Impact on Unaudited Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 122,446	$ 112,194
Prepaid expenses	4,663	4,470
Other non-current assets	9,979	6,403
Total assets	570,544	499,060
Accounts payable	24,437	23,196
Other current liabilities	50,386	38,077
Other non-current liabilities	21,970	16,436
Total liabilities	216,860	132,709
Retained earnings	152,650	128,091
Total stockholders’ equity	353,684	366,351	$ 359,465	$ 348,810
Total liabilities and stockholders’ equity	570,544	$ 499,060
Accounting Standards Update 2014-09 | ASC Topic 606 Impact
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	(6,500)
Prepaid expenses	402
Other non-current assets	(3,970)
Total assets	(10,068)
Accounts payable	(1,581)
Other current liabilities	(4,384)
Other non-current liabilities	(3,407)
Total liabilities	(9,372)
Retained earnings	(696)
Total stockholders’ equity	(696)
Total liabilities and stockholders’ equity	(10,068)
Accounting Standards Update 2014-09 | Without ASC Topic 606 Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	115,946
Prepaid expenses	5,065
Other non-current assets	6,009
Total assets	560,476
Accounts payable	22,856
Other current liabilities	46,002
Other non-current liabilities	18,563
Total liabilities	207,488
Retained earnings	151,954
Total stockholders’ equity	352,988
Total liabilities and stockholders’ equity	$ 560,476