Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies
Restricted cash and other assets	$ 320		$ 320		$ 324
Cash and cash equivalents	94,046		94,046		112,629
Restricted Cash	311		311		311
Cash, cash equivalents and restricted cash	94,357		94,357	$ 74,970	112,940	$ 80,978
Tax expense (benefit)	0	$ 0	0	$ 0
Uncertain tax positions	$ 0		$ 0		$ 0
Practical Expedient, Financing Component			true