Equity (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended		258 Months Ended
	Jul. 21, 2015	Jul. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Equity
Proceed from option exercises			$ 4.5		$ 10.6	$ 21.3
Preferred stock, par value (in dollars per share)			$ 0.001		$ 0.001		$ 0.001	$ 0.001
Common stock, par value (in dollars per share)			0.001		0.001		$ 0.001	$ 0.001
Common stock dividend quarterly declared and paid per share (in dollars per share)			$ 0.40	$ 0.35	$ 0.80	$ 0.70
Share Repurchase Plan
Number of shares repurchased under stock repurchase plan			251,165		3,438,400		20,600,000
Average costs per share			$ 59.97		$ 58.17		$ 29.17
Value of shares repurchased			$ 15.1		$ 200.0
Weighted Average Grant Date Fair Value
Stock options exercised (in shares)			112,175		221,731
Dividends paid			$ 29.7	$ 27.2	$ 60.4	$ 54.4
Subsequent event
Share Repurchase Plan
Number of shares repurchased under stock repurchase plan		1,206,586
Average costs per share		$ 59.11
Value of shares repurchased		$ 71.3
Number of shares authorized by the Board of Directors to be repurchased under stock repurchase plan		2,478,247
Shares outstanding ( as a percent)		3.00%
Weighted Average Grant Date Fair Value
Common stock quarterly dividend per share (in dollars per share)	$ 0.40
Restricted stock
Changes in unvested restricted stock grants and RSUs
Granted (in shares)					12,719
RSU's, 2012 grant
Weighted Average Grant Date Fair Value
Restricted stock units that vested					258,719
RSU's
Changes in unvested restricted stock grants and RSUs
Granted (in shares)					557,760
Weighted Average Grant Date Fair Value
Dividend equivalents					$ 1.0
Performance targets Period					3 years
RSU's | Performance-based
Changes in unvested restricted stock grants and RSUs
Granted (in shares)					225,450
Unvested RSUs and Restricted Stock
Changes in unvested restricted stock grants and RSUs
Unvested at the beginning of the period (in shares)		1,249,525			846,760
Granted (in shares)					570,479
Vested (in shares)					(75,719)
Canceled (in shares)					(91,995)
Unvested at the end of the period (in shares)			1,249,525		1,249,525		1,249,525
Shares reserved for future grants (all plans)					2,088,837
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)		$ 63.31			$ 65.10
Granted (in dollars per shares)					59.42
Vested (in dollars per shares)					58.87
Canceled (in dollars per shares)					58.06
Unvested at the end of the period (in dollars per shares)			$ 63.31		$ 63.31		$ 63.31