Condensed Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues		$ 77,646	$ 58,574	$ 148,942	$ 113,382
Cost of revenues	[1]	40,052	29,303	77,236	56,280
Gross profit		37,594	29,271	71,706	57,102
Operating expenses:
Sales and marketing	[1]	15,866	12,108	31,671	23,074
Research and development	[1]	19,118	11,756	36,775	22,913
General and administrative	[1]	14,079	10,798	27,939	21,094
Acquisition related costs		1,977	258	4,695	514
Amortization of acquired intangibles		905	368	2,120	736
Unoccupied lease charges		0	658	0	658
Total operating expenses		51,945	35,946	103,200	68,989
Loss from operations		(14,351)	(6,675)	(31,494)	(11,887)
Other income (expense):
Interest and other income		856	755	1,663	954
Interest and other expense		(4,073)	(2,860)	(7,087)	(4,082)
Total other income (expense), net		(3,217)	(2,105)	(5,424)	(3,128)
Loss before income taxes		(17,568)	(8,780)	(36,918)	(15,015)
Benefit from income taxes		237	153	276	340
Net loss		(17,331)	(8,627)	(36,642)	(14,675)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale investments		97	2	210	(22)
Foreign currency translation adjustment		(22)	0	(10)	0
Comprehensive loss		$ (17,256)	$ (8,625)	$ (36,442)	$ (14,697)
Net loss per common share, basic and diluted (usd per share)		$ (0.39)	$ (0.20)	$ (0.83)	$ (0.35)
Weighted average common shares outstanding:
Basic and diluted (in shares)		44,978	42,605	44,382	42,389

[1] Includes stock-based compensation expenses as follows:     Three Months Ended June 30,   Six Months Ended June 30,     2019   2018   2019   2018 Cost of revenues   $ 1,428
  $ 1,065
  $ 2,976
  $ 2,080
Sales and marketing   1,596
  1,428
  3,402
  2,654
Research and development   2,473
  1,566
  4,485
  2,922
General and administrative   4,072
  2,945
  7,602
  5,443
Total stock-based compensation expenses   $ 9,569
  $ 7,004
  $ 18,465
  $ 13,099