Income Taxes - Summary of Taxability of Cash Distributions Paid on Common Shares (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Ordinary income	$ 2.98	$ 2.50	$ 2.30
Capital gains	0.17	0.23	0.17
Total	$ 3.15	$ 2.73	$ 2.47