Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended		6 Months Ended
	Aug. 02, 2017	Aug. 01, 2017	Jul. 06, 2017	Jul. 05, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Subsequent Event [Line Items]
Cash dividend declared by board (in usd per share)					$ 0.19	$ 0.15	$ 0.37	$ 0.29
Subsequent Event
Subsequent Event [Line Items]
Cash dividend paid per common share (in usd per share)			$ 0.19
Dividend payable record date	Sep. 15, 2017		May 15, 2017
Cash dividend paid per preferred share (in usd per share)				$ 0.98
Dividends paid preferred share				$ 67.5
Cash dividend declared by board (in usd per share)	$ 0.2
Dividend to be paid date	Oct. 03, 2017
Subsequent Event | Preferred Share
Subsequent Event [Line Items]
Dividend to be paid date		Oct. 02, 2017
Cash dividend declared by board (in usd per share)		$ 0.98
Dividends payable preferred share		$ 67.5
Subsequent Event | Partnerships Exchangeable Units
Subsequent Event [Line Items]
Partnership exchangeable unit (in usd per unit)			$ 0.19