Debt - Debt Summary (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt	$ 10,706,139	$ 11,089,815
GBP
Debt Instrument [Line Items]
Debt	$ 676,732	$ 635,972
Percentage of outstanding debt	6.30%	5.80%
CAD
Debt Instrument [Line Items]
Debt	$ 271,975	$ 266,337
Percentage of outstanding debt	2.50%	2.40%
EUR
Debt Instrument [Line Items]
Debt	$ 4,803,307	$ 4,893,693
Percentage of outstanding debt	44.90%	44.10%
JPY
Debt Instrument [Line Items]
Debt	$ 2,182,119	$ 1,951,844
Percentage of outstanding debt	20.40%	17.60%
USD
Debt Instrument [Line Items]
Debt	$ 2,772,006	$ 3,341,969
Percentage of outstanding debt	25.90%	30.10%