Shareholders' Equity - Summary of Preferred Stock Dividends and Distributions (Detail) - $ / shares							1 Months Ended			3 Months Ended		6 Months Ended
	Jul. 23, 2019	Feb. 25, 2019	Oct. 23, 2018	Jul. 24, 2018	Apr. 24, 2018	Feb. 20, 2018	Apr. 30, 2019	Dec. 31, 2017	[1]	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends Payable [Line Items]
Dividends per Series A Preferred Share										$ 0.4375	$ 0.4375	$ 0.4375	$ 0.8750
Series A Preferred Shares [Member]
Dividends Payable [Line Items]
Declaration Date		Feb. 25, 2019	Oct. 23, 2018	Jul. 24, 2018	Apr. 24, 2018	Feb. 20, 2018	Apr. 30, 2019	Feb. 20, 2018
Record Date		Mar. 29, 2019	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Jun. 28, 2019	Mar. 30, 2018
Payment Date		Apr. 15, 2019	Jan. 14, 2019	Oct. 15, 2018	Jul. 16, 2018	Apr. 16, 2018	Jul. 15, 2019	Apr. 16, 2018
Dividends per Series A Preferred Share		$ 0.43750	$ 0.43750	$ 0.43750	$ 0.43750	$ 0.43750	$ 0.43750	$ 0.15556
Series A Preferred Shares [Member] | Subsequent Event [Member]
Dividends Payable [Line Items]
Declaration Date	Jul. 23, 2019
Record Date	Sep. 30, 2019
Payment Date	Oct. 15, 2019
Dividends per Series A Preferred Share	$ 0.43750

[1] This dividend covers the period from, and including, December 14, 2017 to December 31, 2017.