Debt Facilities - Interest Charges (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Interest expense	$ 478,698,000	$ 392,156,000	$ 299,055,000
Interest capitalized	22,625,000	13,338,000	10,943,000
Interest charges incurred	501,323,000	405,494,000	309,998,000
Interest paid, net of capitalization interest	$ 422,168,000	$ 336,700,000	$ 226,500,000