Summary of Significant Accounting Policies (Restricted Cash) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and cash equivalents in balance sheet	$ 33,674	$ 12,620	$ 9,086	$ 15,256
Restricted cash, current portion in balance sheet	5,674	59	775	1,092
Restricted cash in other assets in balance sheet	342	342	342	342
Total cash, cash equivalents and restricted cash in statements of cash flows	39,690	$ 13,021	10,203	16,690
Accounting Standards Update 2016-18
Total cash, cash equivalents and restricted cash in statements of cash flows			$ 1,117	$ 1,434
Letter of Credit | Accounting Standards Update 2016-18
Restricted cash, current portion in balance sheet	$ 5,600