Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Payroll and benefits	$ 134,785	$ 117,636
Deferred revenue and customer advances	63,196	65,653
Income taxes payable	56,664	37,961
Accrued settlement costs	37,783	35,304
Accrued severance plan obligations (Note 14)	15,190	14,053
Accrued interest	11,873	13,046
Other accrued expenses	55,107	55,016
Total accrued expenses	$ 374,598	$ 338,669