Commitments and Contingencies - Leases and Construction Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum future non-cancelable lease obligations on long-term operating leases
2018	$ 224,359
2019	191,120
2020	156,494
2021	121,881
2022	91,351
Thereafter	424,640
Total	1,209,845
Total rent expense for facility and equipment operating leases	267,400	$ 265,100	$ 214,900
Facility rent expense to unrelated parties	224,200	220,800	165,300
Related party
Minimum future non-cancelable lease obligations on long-term operating leases
2018	5,667
2019	5,811
2020	5,958
2021	6,086
2022	5,981
Thereafter	4,559
Total	34,062
Payments for office rent, leasehold improvements and miscellaneous expenses	6,200	$ 5,000	$ 4,700
Construction Commitments
Construction Commitments
Construction contract commitments	$ 38,600