Basis of Condensed Consolidated Financial Statements (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 123,698	$ 118,804	$ 102,932
Restricted cash included in other assets	7,540		17,423
Restricted cash included in prepaid expenses and other current assets	1,069		0
Total cash, cash equivalents and restricted cash	$ 132,307	$ 129,869	$ 120,355	$ 89,974