Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 644,196	$ 373,173	$ 462,743	$ 370,741
Cash	588,100	367,200
Cash equivalents - money market funds	56,100	6,000
Restricted cash	1,400	1,428
Restricted cash, outstanding letter of credit	1,000	1,000
Restricted cash, guaranteed investment certificate for collateralizing an available credit facility	100	100
Restricted cash, foreign tender requirements	$ 300	$ 300