Fair Value of Senior Notes (Parenthetical) (Detail) - 4.5% Senior Unsecured Notes Due 2026 [Member]	3 Months Ended
Jun. 30, 2017
Fair Value Of Financial Instruments [Line Items]
Debt instrument, interest rate	4.50%
Debt instrument, maturity year	2026

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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