Subsequent Events (Details) - Senior Note - Subsequent Event	Jun. 13, 2017 USD ($)
3.51% Senior Notes Due June 13, 2025
Subsequent Event [Line Items]
Debt issued	$ 150,000,000
Interest rate	3.51%
3.77% Senior Notes due August 22, 2028
Subsequent Event [Line Items]
Debt issued	$ 250,000,000
Interest rate	3.77%

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant