Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 436,715	$ 541,835	$ 430,196	$ 373,173
Cash	380,500	485,700
Cash equivalents - money market funds	56,200	56,100
Restricted cash	5,037	5,032
Restricted cash, letter of credit - foreign taxes	3,700	3,700
Restricted cash, letter of credit - lease agreement	1,000	1,000
Restricted cash, guaranteed investment certificate for collateralizing an available credit facility	100	100
Restricted cash, foreign tender requirements	$ 200	$ 200