Equity - Schedule of Dividend Activity (Detail) - $ / shares		12 Months Ended
	Dec. 14, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Dividends declared per share of common stock	$ 0.62	$ 2.48	$ 2.48	$ 2.28
Percent taxable as ordinary dividends		97.20%	92.77%	92.36%
Percent taxable as capital gain dividends		2.80%	7.23%	7.64%
Percentage of taxable dividend		100.00%	100.00%	100.00%