Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Revenues:
Healthcare	$ 55,979	$ 48,478	$ 48,070	$ 50,370	$ 43,266	$ 42,204	$ 43,814	$ 47,289	$ 202,897	$ 176,573	$ 155,989
Commuter	17,824	17,580	17,383	17,376	15,967	16,003	16,028	15,897	70,163	63,895	61,776
COBRA	23,291	18,670	17,879	15,406	14,187	12,229	12,313	12,570	75,246	51,299	31,996
Other	3,968	4,196	4,393	3,850	9,683	12,724	10,602	9,540	16,407	42,549	18,071
Total revenues	101,062	88,924	87,725	87,002	83,103	83,160	82,757	85,296	364,713	334,316	267,832
Operating expenses:
Cost of revenues (excluding amortization of internal use software)	39,987	30,566	28,411	31,260	28,960	26,364	29,775	32,071	130,224	117,170	100,226
Technology and development, sales and marketing, general and administrative, and employee termination and other charges	44,323	41,972	42,985	38,366	35,687	37,147	39,472	37,281
Amortization and change in contingent consideration	8,013	6,944	11,695	7,445	7,672	6,935	6,732	6,279	34,097	27,618	20,992
Total operating expenses	92,323	79,482	83,091	77,071	72,319	70,446	75,979	75,631	331,967	294,375	236,783
Income from operations	8,739	9,442	4,634	9,931	10,784	12,714	6,778	9,665	32,746	39,941	31,049
Other, net	390	(326)	(306)	(323)	(796)	(281)	(370)	(507)
Income before income taxes	9,129	9,116	4,328	9,608	9,988	12,433	6,408	9,158	32,181	37,987	30,185
Income tax provision	(3,467)	(3,222)	(1,475)	(3,812)	(3,793)	(4,835)	(2,890)	(3,519)	(11,976)	(15,037)	(11,943)
Net income	$ 5,662	$ 5,894	$ 2,853	$ 5,796	$ 6,195	$ 7,598	$ 3,518	$ 5,639	$ 20,205	$ 22,950	$ 18,242
Net income per share:
Basic (in dollars per share)	$ 0.15	$ 0.16	$ 0.08	$ 0.16	$ 0.17	$ 0.21	$ 0.10	$ 0.16	$ 0.56	$ 0.64	$ 0.52
Diluted (in dollars per share)	$ 0.15	$ 0.16	$ 0.08	$ 0.16	$ 0.17	$ 0.21	$ 0.10	$ 0.15	$ 0.54	$ 0.63	$ 0.50
Shares used in computing net income per share:
Basic (in shares)	36,727	36,605	36,361	35,916	35,936	35,880	35,761	35,555	36,404	35,784	35,145
Diluted (in shares)	37,652	37,454	37,195	36,529	36,597	36,516	36,596	36,668	37,210	36,595	36,330