Significant Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 54,435	$ 74,677	$ 38,810
Restricted cash			974
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	55,161	$ 76,444	39,961	$ 39,020
Included In Deposits And Other [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 726		$ 177