Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	May 30, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues		$ 108,986	$ 103,804	$ 97,581	$ 92,380	$ 86,840	$ 79,702	$ 77,646	$ 71,296	$ 402,751		$ 315,484		$ 241,100
Cost of revenues		64,476	57,366	53,203	53,107	44,802	40,447	40,052	37,184	228,152	[1]	162,485	[1]	121,855	[1]
Gross profit		44,510	46,438	44,378	39,273	42,038	39,255	37,594	34,112	174,599		152,999		119,245
Operating expenses:
Sales and marketing		17,726	18,403	16,310	19,884	16,576	15,700	15,866	15,805	72,323	[1]	63,947	[1]	48,124	[1]
Research and development		25,213	23,568	23,642	24,958	19,881	19,617	19,118	17,657	97,381	[1]	76,273	[1]	51,334	[1]
General and administrative		17,061	17,563	17,203	19,110	15,382	13,418	14,079	13,860	70,937	[1]	56,739	[1]	44,990	[1]
Acquisition related costs		500	818	1,127	(1,967)	8,574	2,758	1,977	2,718	478		16,027		4,145
Amortization of acquired intangibles		4,441	4,465	4,491	4,491	3,307	912	905	1,215	17,888		6,339		1,844
Partnership termination charges	$ 5,600	0	0	13,244	0	0	0	0	0	13,244		0		0
Unoccupied lease charges		45	1,468	668	0	176	244	0	0	2,181		420		658
Total operating expenses		64,986	66,285	76,685	66,476	63,896	52,649	51,945	51,255	274,432		219,745		151,095
Loss from operations		(20,476)	(19,847)	(32,307)	(27,203)	(21,858)	(13,394)	(14,351)	(17,143)	(99,833)		(66,746)		(31,850)
Total other income (expense), net		(16,550)	(6,757)	(6,599)	(6,465)	(5,988)	(5,206)	(3,217)	(2,207)	(36,371)		(16,618)		(7,350)
Loss before income taxes		(37,026)	(26,604)	(38,906)	(33,668)	(27,846)	(18,600)	(17,568)	(19,350)	(136,204)		(83,364)		(39,200)
Benefit from (provision for) income taxes		(795)	(116)	(65)	(440)	12,180	31	237	39	(1,416)		12,487		3,803
Net loss		$ (37,821)	$ (26,720)	$ (38,971)	$ (34,108)	$ (15,666)	$ (18,569)	$ (17,331)	$ (19,311)	$ (137,620)		$ (70,877)		$ (35,397)
Net loss per common share, basic and diluted (usd per share)		$ (0.69)	$ (0.50)	$ (0.76)	$ (0.70)	$ (0.32)	$ (0.39)	$ (0.39)	$ (0.44)	$ (2.65)		$ (1.53)		$ (0.83)

[1] Includes stock-based compensation expense as follows:  Year Ended December 31, 202020192018Cost of revenues$9,888 $6,427 $4,773 Sales and marketing8,770 7,740 5,837 Research and development12,869 9,864 6,852 General and administrative17,708 15,347 11,758 Total stock-based compensation expense$49,235 $39,378 $29,220