Derivative Financial Instruments - Summary of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk (Detail) - Cash Flow Hedges [Member] - Designated as Hedging Instrument [Member] £ in Thousands, CAD in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) DerivativeInstrument	Dec. 31, 2016 USD ($) DerivativeInstrument	Dec. 31, 2017 CAD DerivativeInstrument	Dec. 31, 2016 GBP (£) DerivativeInstrument	Dec. 31, 2016 CAD DerivativeInstrument
Interest Rate Caps [Member] | GBP [Member] | GBP LIBOR [Member]
Derivative [Line Items]
Number of Instruments		1		1	1
Notional Amount | £				£ 15,142
Strike		2.00%		2.00%	2.00%
Wtd. Avg. Maturity (Years)		3 months 19 days
Interest Rate Caps [Member] | USD [Member] | USD LIBOR [Member]
Derivative [Line Items]
Number of Instruments	9	21	9	21	21
Notional Amount | $	$ 204,248	$ 802,256
Strike	2.40%	2.00%	2.40%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	1 year 6 months	4 months 24 days
Interest Rate Caps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments	3	5	3	5	5
Notional Amount | CAD			CAD 23,370		CAD 400,035
Strike	2.00%	2.00%	2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	3 months 19 days	4 months 24 days
Interest Rate Swaps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments	4	4	4	4	4
Notional Amount | CAD			CAD 108,094		CAD 108,271
Strike	1.00%	1.00%	1.00%	1.00%	1.00%
Wtd. Avg. Maturity (Years)	1 year 4 months 24 days	2 years 4 months 24 days