Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Accrued expenses	$ 3,037	$ 1,508
Long-lived intangible assets and fixed assets — basis difference	22,146	12,766
Net operating loss carryforwards	68,356	68,395
Stock-based compensation	19,515	15,049
Deferred revenue	4,060	2,828
Convertible note hedge	6,387	10,299
Other	2,276	1,418
Total deferred tax assets	125,777	112,263
Valuation allowance	(111,775)	(96,326)
Deferred tax assets, net of valuation allowance	14,002	15,937
Deferred tax liabilities:
Prepaid expenses and deferred commissions	(7,718)	(7,401)
Convertible note discount	(4,721)	(7,688)
Other	(591)	(612)
Total deferred tax liabilities	(13,030)	(15,701)
Net deferred tax assets (liabilities)	$ 972	$ 236