Equity - Exchangeable Shares and Series F and Series G Preferred Stock (Detail)		3 Months Ended		6 Months Ended
	Oct. 06, 2017 shares	Jun. 30, 2018 shares	Jun. 30, 2017 shares	Jun. 30, 2018 Acquisition shares	Jun. 30, 2017 shares	Dec. 31, 2017 shares	Oct. 05, 2017 shares
Class of Stock [Line Items]
Number of shares of Common stock received for each exchangeable share (in shares)				1
Minimum number of shares that can be exchanged by exchangeable shareholders unless the number of remaining exchangeable shares registered in the name of the holder is less (in shares)				50,000
Number of business acquisitions having issuances of preferred stock | Acquisition				2
Common stock, shares outstanding (in shares)		149,088,134		149,088,134		153,342,326
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)							1
Preferred stock, shares retired (in shares)	1
Series G Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		1		1		1
Preferred stock, shares outstanding (in shares)		1		1		1
Exchangeable Shares For Common Stock
Class of Stock [Line Items]
Exchangeable shares exchanged for common stock (in shares)		0	0	0	2,500,000
Exchangeable Shares
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		486,112		486,112		486,112
Exchangeable Shares Associated with Series G Preferred Stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		400,000		400,000