Supplemental Disclosures to Consolidated Statements of Cash Flows (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 88,292	$ 170,741	$ 573,210
Restricted cash included in other current assets	6,630	775	938
Total cash and cash equivalents and restricted cash at end of period	$ 94,922	$ 171,516	$ 574,148	$ 488,127