Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (32,849)	$ (41,708)	$ (64,911)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	22,391	23,169	17,267
Deferred income taxes	(2,182)	581	581
Bad debt expense and other reserves	1,385	1,285	925
Stock-based compensation	32,241	24,739	42,563
Common stock warrant expense (benefit)	0	46	(803)
Non-cash interest expense on lease financing obligation	370	396	0
Write-off and loss on disposal of fixed assets	194	474	1,631
Changes in operating assets and liabilities:
Accounts receivable	(3,687)	(4,391)	(5,938)
Prepaid expenses	569	4	(855)
Other current assets	765	(846)	1,087
Other assets	162	(613)	(458)
Accounts payable	4,803	(4,552)	5,312
Accrued employee expenses	(2,683)	1,152	(6,510)
Accrued expenses and other current liabilities	(479)	1,531	(1,781)
Other liabilities	1,118	1,501	521
Net cash provided by (used in) operating activities	22,118	2,768	(11,369)
Cash flows from investing activities
Purchase of property and equipment	(19,809)	(16,639)	(29,836)
Net cash used in investing activities	(19,809)	(16,639)	(29,836)
Cash flows from financing activities
Proceeds from public offering, net of underwriting discounts and offering costs	17,398	0	0
Repurchase of common stock option awards	0	(100)	0
Proceeds from exercise of common stock options	73,543	9,112	6,328
Taxes paid related to net share settlement of equity awards	(3,209)	(1,312)	(908)
Proceeds from financing obligation drawdown	0	1,521	622
Payments for lease financing obligation	0	0	(5)
Net cash provided by financing activities	87,732	9,221	6,037
Net increase (decrease) in cash and cash equivalents	90,041	(4,650)	(35,168)
Cash and cash equivalents at beginning of period	107,721	112,371	147,539
Cash and cash equivalents at end of period	197,762	107,721	112,371
Cash paid during the year for:
Interest	2,099	2,133	617
Income taxes	43	82	48
Supplemental disclosures of non-cash activities
Stock-based compensation capitalized for software development	1,407	1,012	1,325
Recognition of leased facility asset and lease financing obligation	0	0	23,683
Capitalized assets included in accounts payable, accrued employee expenses and other accrued expenses	$ 1,980	$ 1,078	$ 1,635