Goodwill - Schedule of Reporting Units Goodwill Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill balance as of 12/31/2017	$ 6,610,279	$ 6,015,375	$ 5,896,215
Percentage change in operating income used to evaluate fair value of reporting unit for goodwill assessment	3.00%
Percentage change in operating income used to evaluate fair value of reporting unit for goodwill assessment	1.00%
GERMANY
Goodwill [Line Items]
Goodwill balance as of 12/31/2017	$ 316,369
Carrying amount coverage	13.70%
Sensitivities, Operating Income	(1.60%)
Sensitivities, Discount rate	(11.10%)
PORTUGAL
Goodwill [Line Items]
Goodwill balance as of 12/31/2017	$ 46,713
Carrying amount coverage	16.90%
Sensitivities, Operating Income	(1.90%)
Sensitivities, Discount rate	(6.00%)
POLAND
Goodwill [Line Items]
Goodwill balance as of 12/31/2017	$ 46,610
Carrying amount coverage	11.80%
Sensitivities, Operating Income	(1.90%)
Sensitivities, Discount rate	(6.00%)