Summary of Significant Accounting Policies Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 59,321	$ 118,564	$ 258,567	$ 159,678
Restricted cash	560	55	47	0
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 59,881	$ 118,619	$ 258,614	$ 159,678