Recent Accounting Standards (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017		Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	[1]
Recent Accounting Standards [Abstract]
Restricted Cash	$ 28,963
Cash, cash equivalents and restricted cash at end of period	142,443	[1]	$ 372,608	$ 214,170	$ 116,370
Increase in net cash provided by operating activities	$ 473

[1] Balances were adjusted due to the adoption of Financial Accounting Standards Board Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash" as discussed in further detail in Note 2. "Recent Accounting Standards."