Real Estate - Summary of Acquisition (Detail) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft² Property	Dec. 31, 2016 USD ($) ft² Property	Dec. 31, 2015 USD ($) ft² Property
Real Estate [Abstract]
Number of operating properties | Property	16	9	52
Square feet | ft²	6,859	1,823	7,375
Acquisition value of net investments in real estate properties | $	$ 1,139,410	$ 411,706	$ 1,042,562