Summary of Significant Accounting Policies - (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Reconciliation of Cash, Cash Equivalents, and Restricted Cash
Cash and cash equivalents	$ 330,099			$ 931,751	$ 1,039,591	$ 657,688
Restricted cash included in deferred expenses and other assets, net	64,154			42,793	27,399	20,045
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows	394,253			$ 974,544	$ 1,066,990	$ 677,733
New Accounting Pronouncements
Operating lease right-of-use assets	28,908
Finance lease right-of-use asset	67,901
Operating lease liabilities	28,917
Finance lease liability	$ 68,571
ASU No. 2016-02
New Accounting Pronouncements
Operating lease right-of-use assets			$ 31,600
Finance lease right-of-use asset		$ 68,100
Operating lease liabilities			$ 31,600
Finance lease liability		$ 68,100