Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Operations
Revenue	$ 43,252	$ 37,092	$ 35,238	$ 34,612	$ 30,756	$ 28,407	$ 24,744	$ 26,332	$ 150,194	$ 110,239	$ 83,127
Costs and expenses:
Servicing and support	8,749	7,845	7,903	7,550	7,012	6,598	7,000	6,248	32,047	26,858	22,718
Technology and content development	7,529	7,082	6,466	6,134	5,403	5,726	5,818	5,674	27,211	22,621	19,472
Program marketing and sales	20,231	21,567	21,526	19,587	16,296	16,971	16,710	15,241	82,911	65,218	54,103
General and administrative	10,064	8,477	8,871	6,711	5,973	6,303	5,708	5,436	34,123	23,420	14,840
Total costs and expenses	46,573	44,971	44,766	39,982	34,684	35,598	35,236	32,599	176,292	138,117	111,133
Loss from operations	(3,321)	(7,879)	(9,528)	(5,370)	(3,928)	(7,191)	(10,492)	(6,267)	(26,098)	(27,878)	(28,006)
Other income (expense):
Interest expense	(173)	(127)	(126)	(126)	(119)	(176)	(134)	(784)	(552)	(1,213)	27
Interest income	94	21	24	28	30	30	31	1	167	92	26
Other		(250)							(250)
Total other income (expense)	(79)	(356)	(102)	(98)	(89)	(146)	(103)	(783)	(635)	(1,121)	53
Loss before income taxes									(26,733)	(28,999)	(27,953)
Net loss	$ (3,400)	$ (8,235)	$ (9,630)	$ (5,468)	$ (4,017)	$ (7,337)	$ (10,595)	$ (7,050)	(26,733)	(28,999)	(27,953)
Preferred stock accretion										(89)	(347)
Net loss attributable to holders of common stock									$ (26,733)	$ (29,088)	$ (28,300)
Net loss per share attributable to holders of common stock, basic and diluted (in dollars per share)	$ (0.07)	$ (0.20)	$ (0.23)	$ (0.13)	$ (0.10)	$ (0.18)	$ (0.27)	$ (0.92)	$ (0.63)	$ (0.91)	$ (3.81)
Weighted-average shares of common stock outstanding, basic and diluted (in shares)	45,651,475	41,645,894	41,362,476	40,978,741	40,577,087	40,269,937	39,304,884	7,698,709	42,420,356	32,075,107	7,432,055