Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Accruals and reserves	$ 30,317	$ 41,094
Deferred revenue	65,016	95,969
Tax credits	80,772	50,072
Net operating losses	36,674	41,986
Stock based compensation	21,714	34,349
Transaction costs	0	557
Depreciation and amortization	4,939	1,933
Other	0	267
Valuation allowance	(76,789)	(14,156)
Total deferred tax assets	162,643	252,071
Deferred tax liabilities:
Acquired technology	(2,882)	(8,524)
Prepaid expenses	(7,414)	(11,119)
Other	(222)	0
Total deferred tax liabilities	(10,518)	(19,643)
Total net deferred tax assets	$ 152,125	$ 232,428