Significant Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 74,677	$ 38,837	$ 29,366	$ 24,741
Restricted cash	1,023	0	0	257
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	76,444	39,020	29,568	25,317	$ 25,317
Included In Deposits And Other [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 744	$ 183	$ 202	$ 319