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The Company and Summary of Significant Accounting Policies (Details) $ in Thousands, £ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 GBP (£)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Reclassification
Operating Lease, Right-of-Use Asset							$ 27,043
Share-based Compensation				$ 25,163	$ 22,672
Capitalization of internally developed software costs		$ 100		$ 500
Capitalized Computer Software, Unamortized							1,600	$ 1,200
Amortization expense for capitalized internally developed software			$ 100
Investment in privately held company			2,500		2,500
Retained earnings							13,335	27,964
Restricted cash			$ 1,200		$ 1,200		1,200	$ 1,200
Operating Lease, Liability							37,633
Capitalized Computer Software, Amortization Period				3 years
Advance Royalties							$ 600
Operating Leases
Reclassification
Operating Lease, Right-of-Use Asset	$ 30,800
Operating Lease, Liability	41,600
Deferred Rent Receivables, Net	(3,900)
Tenant Improvement Allowance	$ 6,900
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Euro [Member]
Reclassification
Derivative, notional amount \| £						£ 19.9
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Pound [Member]
Reclassification
Derivative, notional amount \| £						£ 9.8
Performance Shares [Member]
Reclassification
Share-based Compensation		$ 200		$ 700