Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Healthcare	$ 39,813	$ 38,600	$ 37,592	$ 39,984	$ 32,896	$ 32,646	$ 33,871	$ 35,727	$ 155,989	$ 135,140	$ 112,905
Commuter	15,605	15,078	15,050	16,043	15,201	14,949	14,722	14,707	61,776	59,579	51,817
COBRA	14,713	9,544	3,701	4,038	4,045	3,837	3,673	3,492	31,996	15,047	8,157
Other	8,326	4,776	2,414	2,555	2,889	2,139	2,295	2,189	18,071	9,512	4,403
Total revenue	78,457	67,998	58,757	62,620	55,031	53,571	54,561	56,115	267,832	219,278	177,282
Operating expenses:
Cost of revenues (excluding amortization of internal use software)	31,321	24,951	21,157	22,797	22,073	19,300	19,932	20,613	100,226	81,918	64,647
Sales and marketing, technology and development and general and administrative	35,127	30,771	25,169	24,498	23,232	23,832	23,167	23,541
Amortization and change in contingent consideration	6,335	5,688	4,549	4,420	1,871	554	4,725	4,462	20,992	11,612	15,674
Total operating expenses	72,783	61,410	50,875	51,715	47,176	43,686	47,824	48,616	236,783	187,302	158,350
Income from operations	5,674	6,588	7,882	10,905	7,855	9,885	6,737	7,499	31,049	31,976	18,932
Other income (expense):
Other, net	(594)	215	(242)	(243)	(57)	(316)	(349)	(352)
Income before income taxes	5,080	6,803	7,640	10,662	7,798	9,569	6,388	7,147	30,185	30,902	17,625
Income tax provision	(1,982)	(2,690)	(3,053)	(4,218)	(2,478)	(1,818)	(2,396)	(2,511)	(11,943)	(9,203)	(7,126)
Net income	$ 3,098	$ 4,113	$ 4,587	$ 6,444	$ 5,320	$ 7,751	$ 3,992	$ 4,636	$ 18,242	$ 21,699	$ 10,499
Net income per share attributable to common stockholders:
Basic	$ 0.09	$ 0.12	$ 0.13	$ 0.19	$ 0.15	$ 0.23	$ 0.12	$ 0.14	$ 0.52	$ 0.65	$ 0.45
Diluted	$ 0.08	$ 0.11	$ 0.13	$ 0.18	$ 0.15	$ 0.22	$ 0.11	$ 0.14	$ 0.50	$ 0.62	$ 0.33
Shares Outstanding
Shares used in basic net income per share calculations	35,393	35,234	35,117	34,831	34,638	34,134	33,473	32,226	35,145	33,626	18,138
Shares used in diluted net income per share calculations	36,517	36,152	36,340	36,303	36,313	35,785	35,047	33,841	36,330	35,277	24,414