Debt - Debt Summary (Parenthetical) (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt	$ 10,968,320	$ 11,089,815
GBP
Debt Instrument [Line Items]
Debt	$ 656,208	$ 635,972
Percentage of outstanding debt	6.00%	5.80%
CAD
Debt Instrument [Line Items]
Debt	$ 277,564	$ 266,337
Percentage of outstanding debt	2.50%	2.40%
EUR
Debt Instrument [Line Items]
Debt	$ 5,003,393	$ 4,893,693
Percentage of outstanding debt	45.60%	44.10%
JPY
Debt Instrument [Line Items]
Debt	$ 2,113,373	$ 1,951,844
Percentage of outstanding debt	19.30%	17.60%
USD
Debt Instrument [Line Items]
Debt	$ 2,917,782	$ 3,341,969
Percentage of outstanding debt	26.60%	30.10%