Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 462,743	$ 370,741	$ 368,270	$ 376,727
Restricted cash	1,454	1,446
Restricted cash, collateral for outstanding letters of credit		1,000
Restricted cash, guaranteed investment certificate for collateralizing an available credit facility	200	100
Restricted cash, foreign tender requirements	300	300
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	456,700	364,700
Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 6,000	$ 6,000