Other Balance Sheet Accounts Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Receivables under transition service agreements	$ 14,288	$ 7,509
Income taxes receivable	10,593	3,806
Prepaid expenses	5,615	2,898
Other	805	162
Total prepaid expenses and other current assets	$ 31,301	$ 14,375