Shareholders' Equity - Summary of Dividends Reflected for U.S. Federal Income Tax Purposes (Detail) - $ / shares									6 Months Ended	12 Months Ended
	Oct. 24, 2017	Jul. 25, 2017	Apr. 25, 2017	Feb. 28, 2017	Nov. 01, 2016	Aug. 02, 2016	May 03, 2016	Mar. 08, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Dividends Payable [Line Items]
Total	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.50	$ 1.00	$ 1.00
Federal Income Tax [Member] | Dividend Declared [Member]
Dividends Payable [Line Items]
Ordinary income									0.50	0.53	1.00
Capital gain distributions									0	0.47	0
Return of capital									0	0	0
Total									$ 0.50	$ 1.00	$ 1.00