CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 258,031	$ 236,634	$ 216,007
Cost of revenue	88,649	82,178	71,791
Gross profit	169,382	154,456	144,216
Operating expenses:
Research and development	22,247	21,547	19,868
Sales and marketing	123,374	111,376	105,635
General and administrative	57,218	56,264	54,983
Total operating expenses	202,839	189,187	180,486
Loss from operations	(33,457)	(34,731)	(36,270)
Other expense, net:
Foreign currency transaction gain (loss)	1,802	(2,430)	(1,813)
Interest expense	(6,964)	(4,425)	(941)
Total other expense, net	(5,162)	(6,855)	(2,754)
Loss before income taxes	(38,619)	(41,586)	(39,024)
Income tax (benefit) expense	(1,474)	74	192
Net loss	$ (37,145)	$ (41,660)	$ (39,216)
Net loss per share
Basic and diluted (in dollars per share)	$ (0.87)	$ (1.00)	$ (0.97)
Weighted average common shares outstanding:
Basic and diluted (in shares)	42,739,525	41,729,013	40,237,848