Segment Information - Summary of Financial Information by Operating Segment, Goodwill (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Goodwill:
Beginning balance	$ 2,681,188
Increase from 2017 acquisition	15,302
Foreign currency translation	60,770
Purchase price allocation and other	(6,086)
Ending balance	2,751,174
U.S. Facilities [Member] | Operating Segment [Member]
Goodwill:
Beginning balance	2,041,795
Purchase price allocation and other	797
Ending balance	2,042,592
U.K. Facilities [Member] | Operating Segment [Member]
Goodwill:
Beginning balance	639,393
Increase from 2017 acquisition	15,302
Foreign currency translation	60,770
Purchase price allocation and other	(6,883)
Ending balance	$ 708,582