Summary of Significant Accounting Policies - Cash flow statement as adjusted (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Initial Application Period [Line Items]
Other investing activities	$ 462	$ (850)
Net cash provided by (used in) investing activities	109,269	(148,462)
Net increase (decrease) in cash, cash equivalent, and restricted cash		(131,412)
Cash, cash equivalents, and restricted cash at beginning of the period	450,125	393,019
Cash, cash equivalents, and restricted cash at end of the period	$ 498,619	261,607
As Previously Reported
Initial Application Period [Line Items]
Other investing activities		2,314
Net cash provided by (used in) investing activities		(145,298)
Net increase (decrease) in cash, cash equivalent, and restricted cash		(128,248)
Cash, cash equivalents, and restricted cash at beginning of the period		389,275
Cash, cash equivalents, and restricted cash at end of the period		261,027
Accounting Standards Update 2016-18 | Adjustment
Initial Application Period [Line Items]
Other investing activities		(3,164)
Net cash provided by (used in) investing activities		(3,164)
Net increase (decrease) in cash, cash equivalent, and restricted cash		(3,164)
Cash, cash equivalents, and restricted cash at beginning of the period		3,744
Cash, cash equivalents, and restricted cash at end of the period		$ 580