Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Statement of Cash Flows [Abstract]
Net loss	$ (14,855)	$ (26,322)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	11,747	11,677
Deferred income taxes	288	281
Bad debt expense and other reserves	789	590
Stock-based compensation	12,753	11,792
Non-cash interest expense on lease financing obligation	233	411
Write-off and loss on disposal of fixed assets	36	392
Changes in operating assets and liabilities:
Accounts receivable	(978)	463
Prepaid expenses	(1,006)	(1,304)
Other current assets	730	(196)
Other assets	(106)	(316)
Accounts payable	4,248	(4,364)
Accrued employee expenses	(2,148)	1,156
Accrued expenses and other liabilities	(115)	2,372
Other liabilities	1,103	1,301
Net cash provided by (used in) operating activities	12,719	(2,067)
Cash flows from investing activities
Purchase of property and equipment	(10,340)	(9,785)
Net cash used in investing activities	(10,340)	(9,785)
Cash flows from financing activities
Proceeds from public offering, net of underwriting discounts and offering costs	17,398	0
Repurchase of common stock option awards	0	(100)
Proceeds from exercise of common stock options	55,534	1,571
Taxes paid related to net share settlement of equity awards	(1,310)	(391)
Proceeds from financing obligation drawdown	0	1,521
Net cash provided by financing activities	71,622	2,601
Net increase (decrease) in cash and cash equivalents	74,001	(9,251)
Cash and cash equivalents at beginning of period	107,721	112,371
Cash and cash equivalents at end of period	181,722	103,120
Supplemental disclosures of non-cash activities
Stock-based compensation capitalized for software development	550	468
Capitalized assets included in accounts payable, accrued employee expenses and other accrued expenses	842	61
Proceeds receivable from exercise of stock options included in other current assets	149	0
Taxes payable related to net share settlement of equity awards included in accrued employee expenses	$ 266	$ 0