Accrued Expenses and Other Current Liabilities (Schedule of Accrued Expenses and Other Current Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued compensation and employee benefits	$ 161,049	$ 143,666
Other accrued expenses	116,630	113,133
Total	$ 277,679	$ 256,799