Summary of Significant Accounting Policies Cash, Cash Equivalent, and Restricted Cash (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 109,044	$ 140,938	$ 109,044	$ 120,221
Restricted cash included in other current assets	51	0	51	51
Long-term restricted cash	2,055	762	2,055	2,056
Total cash, cash equivalents, and restricted cash	111,150	141,700	111,150	$ 122,328	$ 487,335
Proceeds from borrowings		$ 50,000	$ 761,938
Improper Netting Within Financing Activities On Cash Flow Statement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Proceeds from borrowings	$ 150,000