Income Taxes - Components Of Company's Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Net operating loss carryforwards	$ 17,301	$ 40,969
Research tax credit	15,433	9,642
Foreign tax credit	12,479	7,201
Expenses not currently deductible	13,031	5,193
Basis difference in fixed and intangible assets	3,200	3,529
Gross deferred tax assets	61,444	66,534
Valuation allowance	(32,032)	(12,846)
Net deferred tax assets	29,412	53,688
Deferred tax liabilities
Acquired intangible assets, domestic	(34,408)	(70,338)
Acquired intangible assets, foreign	(4,903)	(13,045)
Unremitted earnings of foreign subsidiaries	(30)	(129)
Net deferred tax liabilities	$ (9,929)	$ (29,824)