Summary Of Significant Accounting Policies - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash, Cash Equivalents, and Restricted Cash
Restricted cash	$ 1,600	$ 1,600	$ 300
Cash and cash equivalents	146,630	185,323	143,180
Restricted cash included in "Prepaid expenses and other current assets"			320
Restricted cash included in "Restricted cash and other non-current assets"	1,619	1,619
Total	$ 148,249	$ 186,942	$ 143,500	$ 10,983