Debt - Summary of Debt (Parenthetical) (Detail)	Mar. 31, 2019 USD ($)
7.00% Senior Notes 2019 [Member]
Debt Instrument [Line Items]
Senior notes, issued at par percentage	98.238%
3.80% Senior Notes 2025 [Member]
Debt Instrument [Line Items]
Senior notes, issued at par percentage	99.975%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Aggregate maximum borrowing capacity	$ 500,000,000
Line of credit facility maximum borrowing capacity increased amount subject to obtaining commitments	$ 750,000,000