Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue	$ 166,371	$ 159,079	$ 161,741	$ 163,332	$ 162,072	$ 151,575	$ 156,584	$ 153,019		$ 650,523	$ 623,250	$ 557,111
Operating expenses:
Cost of revenue	71,797	68,635	68,526	69,218	68,829	66,461	67,891	64,490		278,176	267,671	233,102
Sales & marketing	47,182	45,614	44,488	44,446	43,034	41,028	42,018	40,368		181,730	166,448	146,464
Product development	15,103	13,533	13,594	14,986	11,689	14,032	16,728	16,448		57,216	58,897	52,486
General and administrative	26,486	28,114	32,063	26,583	22,881	23,355	24,322	27,224		113,246	97,782	98,710
Total operating expenses	160,568	155,896	158,671	155,233	146,433	144,876	150,959	148,530		630,368	590,798	530,762
Income from operations	5,803	3,183	3,070	8,099	15,639	6,699	5,625	4,489		20,155	32,452	26,349
Gain on Sale of Webdam	0	0	0	0	0	0	0	38,613		0	38,613	0
Other income / (expense), net	2,816	465	584	896	1,048	217	(7,019)	802		4,761	(4,952)	3,732
Income before income taxes	8,619	3,648	3,654	8,995	16,687	6,916	(1,394)	43,904		24,916	66,113	30,081
Provision / (Benefit) for income tax	4,266	(1,286)	355	1,473	1,774	(531)	(1,140)	11,323		4,808	11,426	13,354
Net income	$ 4,353	$ 4,934	$ 3,299	$ 7,522	$ 14,913	$ 7,447	$ (254)	$ 32,581		$ 20,108	$ 54,687	$ 16,727
Net income per common share:
Basic (in dollars per share)	$ 0.12	$ 0.14	$ 0.09	$ 0.21	$ 0.43	$ 0.21	$ (0.01)	$ 0.94		$ 0.57	$ 1.57	$ 0.48
Diluted (in dollars per share)	$ 0.12	$ 0.14	$ 0.09	$ 0.21	$ 0.42	$ 0.21	$ (0.01)	$ 0.92		$ 0.57	$ 1.54	$ 0.47
Weighted average shares outstanding:
Basic (in shares)	35,478	35,309	35,232	35,114	35,047	34,991	34,913	34,784		35,285	34,935	34,627
Diluted (in shares)	35,786	35,541	35,504	35,491	35,421	35,570	34,913	35,318		35,581	35,420	35,291
Equity-based compensation										$ 22,815	$ 23,869	$ 24,958
Impact of remeasuring deferred tax balances									$ 3,700
Transition tax expense									$ 800
Restatement Adjustment
Operating expenses:
General and administrative							$ 800
Enterprise
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue										$ 258,282	$ 254,809	$ 208,713
Enterprise | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue						$ (800)	$ 400