Debt - Fair Values of Senior Notes and Outstanding Debt under Credit Facility (Parenthetical) (Detail) - 5 1/2% Senior Notes Due 2021 [Member]	3 Months Ended
Mar. 31, 2019
Debt Instrument [Line Items]
Debt instrument, Interest rate	5.50%
Debt instrument, Maturity	2021

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant