Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
New Accounting Pronouncement, Early Adoption
Adjustment to retained earnings	$ (9,144)
Decrease in retained earnings	(1,006,500)	$ (1,423,154)
Accounting Standards Update 2016-16
New Accounting Pronouncement, Early Adoption
Adjustment to retained earnings	(34,132)
Decrease in deferred tax asset	34,100
Accounting Standards Update 2016-01
New Accounting Pronouncement, Early Adoption
Adjustment to retained earnings	$ 9,144