Summary of Significant Accounting Policies (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 931,751	$ 657,688	$ 328,744	$ 711,101
Restricted cash included in deferred expenses and other assets, net	42,793	20,045	25,883	26,657
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows	$ 974,544	$ 677,733	$ 354,627	$ 737,758