Equity (Details) $ / shares in Units, $ in Millions			3 Months Ended	6 Months Ended
	May. 14, 2015 USD ($) shares	Apr. 02, 2015 USD ($)	Jun. 30, 2015 $ / shares shares	Jun. 30, 2015 item shares
Equity
Period common stock is authorized to repurchase		24 months
Shares repurchased (in shares)			1,903,340
Average share price repurchased (in dollars per share) | $ / shares			$ 180.19
Operating Partnership | Limited Partner
Equity
Units Redeemed (in units)	944,359
Value of units redeemed | $	$ 162.7
Partnership agreement of Operating Partnership | Limited Partner
Equity
Exchange of limited partner units, common shares				486,702
Number of limited partners who received common stock | item				8
Maximum
Equity
Common stock authorized for repurchase | $		$ 2,000.0