Business and Significant Accounting Policies - Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 156,368	$ 538,908	$ 474,233	$ 372,976
Restricted cash classified in:
Prepaid expenses and other current assets	2,295	15,148	25,121	13,505
Other assets	0	3,002	0	25,626
Cash and cash equivalents	0	10,000	0	0
Cash and cash equivalents and restricted cash	$ 158,663	$ 567,058	$ 499,354	$ 412,107