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, £ in Thousands, CAD in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) DerivativeInstrument	Dec. 31, 2015 USD ($) DerivativeInstrument	Sep. 30, 2016 GBP (£) DerivativeInstrument	Sep. 30, 2016 CAD DerivativeInstrument	Dec. 31, 2015 GBP (£) DerivativeInstrument	Dec. 31, 2015 EUR (€) DerivativeInstrument	Dec. 31, 2015 CAD DerivativeInstrument
Interest Rate Caps [Member] | USD [Member] | USD LIBOR [Member]
Derivative [Line Items]
Number of Instruments	25	26	25	25	26	26	26
Notional Amount | $	$ 1,086,261	$ 1,097,632
Strike	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	7 months 6 days	1 year 3 months 18 days
Interest Rate Caps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments	6	7	6	6	7	7	7
Notional Amount | CAD				CAD 439,320			CAD 483,286
Strike	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	7 months 6 days	1 year 2 months 12 days
Interest Rate Caps [Member] | EUR [Member] | EURIBOR [Member]
Derivative [Line Items]
Number of Instruments		1			1	1	1
Notional Amount | €						€ 152,710
Strike		2.00%			2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)		1 year
Interest Rate Caps [Member] | GBP [Member] | GBP LIBOR [Member]
Derivative [Line Items]
Number of Instruments	1	1	1	1	1	1	1
Notional Amount | £			£ 15,142		£ 15,142
Strike	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	7 months 6 days	1 year 3 months 18 days
Interest Rate Swaps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments	2		2	2
Notional Amount | CAD				CAD 17,273
Strike	1.00%		1.00%	1.00%
Wtd. Avg. Maturity (Years)	3 years 10 months 24 days