Summary of Significant Accounting Policies Cash, Cash Equivalent, and Restricted Cash (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 162,882	$ 135,736	$ 162,882	$ 120,221
Restricted cash included in other current assets	51	51	51	51
Long-term restricted cash	2,109	2,066	2,109	2,056
Total cash, cash equivalents, and restricted cash	165,042	137,853	165,042	$ 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