Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Cash Flows [Abstract]
Net loss	$ (15,677)	$ (14,855)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	10,818	11,747
Deferred income taxes	(120)	288
Bad debt expense and other reserves	811	789
Stock-based compensation	18,069	12,753
Non-cash interest expense on lease financing obligation	218	233
Write-off and loss on disposal of fixed assets	143	36
Changes in operating assets and liabilities:
Accounts receivable	(4,491)	(978)
Prepaid expenses	(2,882)	(1,006)
Other current assets	(787)	730
Other assets	(835)	(106)
Accounts payable	(232)	4,248
Accrued employee expenses	106	(2,148)
Accrued expenses and other liabilities	3,033	(115)
Other liabilities	393	1,103
Net cash provided by operating activities	8,567	12,719
Cash flows from investing activities
Purchase of property and equipment	(9,615)	(10,340)
Net cash used in investing activities	(9,615)	(10,340)
Cash flows from financing activities
Proceeds from public offering, net of underwriting discounts and offering costs	0	17,398
Proceeds from exercise of common stock options	3,196	55,534
Taxes paid related to net share settlement of equity awards	(1,423)	(1,310)
Net cash provided by financing activities	1,773	71,622
Net increase in cash and cash equivalents	725	74,001
Cash and cash equivalents at beginning of period	197,762	107,721
Cash and cash equivalents at end of period	198,487	181,722
Supplemental disclosures of non-cash activities
Stock-based compensation capitalized for software development	807	550
Capitalized assets included in accounts payable, accrued employee expenses and other accrued expenses	554	842
Proceeds receivable from exercise of stock options included in other current assets	1	149
Taxes payable related to net share settlement of equity awards included in accrued employee expenses	$ 29	$ 266