Summary of Significant Accounting Policies Reconciliation (Details) - USD ($) $ in Thousands		Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents			$ 615,906	$ 313,943
Restricted cash			0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations	[1]		$ 615,906	$ 313,943	$ 559,521	$ 12,372
Accounting Standards Update 2018-02 [Member]
Prior Period Adjustments Restatement [Line Items]
Cumulative effect of accounting change		$ 3,000

[1] (1) Refer to Note 1 - Summary of Significant Accounting Policies for a reconciliation of cash, cash equivalents, and restricted cash reported to the amounts reported within the accompanying unaudited condensed consolidated balance sheets (“accompanying balance sheets”).