Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 29,632	$ 10,380	$ 7,808	$ 11,012
Restricted cash	1,212	693	1,058	1,078
Restricted cash for Development Projects	33,799	41,982	7,605	26,384
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 64,643	$ 53,055	$ 16,471	$ 38,474