Schedule III - Reconciliation of Real Estate (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Balance at beginning of period		$ 1,734,892,000	$ 1,668,351,000
Additions		257,933,000	69,726,000
Impairments	$ 0	0	0
Dispositions		(71,117,000)	0
Write-offs		(67,665,000)	(3,185,000)
Balance at end of period	$ 1,668,351,000	$ 1,854,043,000	$ 1,734,892,000