Debt (Details) (USD $)	1 Months Ended	12 Months Ended
	Sep. 30, 2014	Jan. 31, 2015		Feb. 01, 2014
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount		$ 1,600,000
Proceeds from Debt, Net of Issuance Costs	246,000,000
Number of unsecured senior notes held		3		2
Unsecured senior notes		398,375,000		150,000,000
Unsecured senior notes estimated fair value		442,000,000		182,000,000
Line of Credit Facility, Fair Value of Amount Outstanding		0
Collateral trust		56,300,000		47,200,000
Trade Letters Of Credit [Member]
Debt Instrument [Line Items]
Trade Letters Of Credit Amount		32,800,000		31,600,000
3.375% Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Proceeds from Debt Issuance, Net of Debt Discount, Percent	99.329%
Unsecured senior notes		248,375,000	[1]	0
Unsecured senior notes due date		Sep. 01, 2024
Unsecured senior notes interest rate	3.375%
Debt Instrument, Face Amount	250,000,000
Unsecured Series A and B Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		150,000,000
Series A Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Unsecured senior notes		85,000,000		85,000,000
Unsecured senior notes due date		Dec. 01, 2018
Unsecured senior notes interest rate		6.38%
Debt Instrument, Face Amount		85,000,000
Series B Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Unsecured senior notes		65,000,000		65,000,000
Unsecured senior notes due date		Dec. 01, 2021
Unsecured senior notes interest rate		6.53%
Debt Instrument, Face Amount		65,000,000
Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity for revolving credit facility		600,000,000
Revolving credit facility expiration date		Jun. 01, 2017
Sublimit for issuance of standby letters of credit		300,000,000
Basis points margin over LIBOR		1.00%
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Standby letter of credit, amount outstanding		19,500,000		24,300,000
New York City Office [Member]
Debt Instrument [Line Items]
Sales and purchase agreement, property purchase price agreed upon	$ 222,000,000

[1] Net of unamortized discount of $1.6 million at January 31, 2015.