CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net revenues:
Net revenues	$ 410,926	$ 321,084	$ 255,066
Cost of revenues:
Cost of revenues	92,182	79,996	80,175
Gross profit	318,744	241,088	174,891
Operating expenses:
Research and development	139,772	114,291	81,926
Sales and marketing	63,569	54,714	51,240
General and administrative	97,489	77,714	64,411
Restructuring charges	97	589	1,047
Gain on liquidation of textbooks	0	0	(4,766)
Total operating expenses	300,927	247,308	193,858
Income (loss) from operations	17,817	(6,220)	(18,967)
Interest expense, net and other income, net:
Interest expense, net	(44,851)	(11,225)	(74)
Other income, net	20,063	3,987	560
Total interest expense, net and other income, net	(24,788)	(7,238)	486
Loss before provision for income taxes	(6,971)	(13,458)	(18,481)
Provision for income taxes	2,634	1,430	1,802
Net loss	$ (9,605)	$ (14,888)	$ (20,283)
Net loss per share, basic and diluted (in dollars per share)	$ (0.08)	$ (0.13)	$ (0.20)
Weighted average shares used to compute net loss per share, basic and diluted (in shares)	119,204	113,251	100,022