Equity Incentive Compensation Plans (Details) (USD $)	3 Months Ended		6 Months Ended			1 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Stock Options	Mar. 31, 2011 Stock Options Executive officers and other officers
Equity Incentive Compensation Plans
Total compensation cost	$ 2,200,000	$ 1,800,000	$ 5,100,000	$ 4,100,000
Stock options activity
Outstanding at the beginning of the period (in shares)					2,017,225
Granted (in shares)					89,865	89,865
Exercised (in shares)					(229,685)
Outstanding at the end of the period (in shares)					1,877,405
Stock options, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)					$ 25.87
Granted (in dollars per share)					$ 48.50
Exercised (in dollars per share)					$ 14.93
Outstanding at the end of the period (in dollars per share)					$ 28.29
Stock options, Aggregate Intrinsic Value
Outstanding at the beginning of the period					35,974,000
Outstanding at the end of the period					46,637,000
Stock options, Number of Shares Exercisable
Options outstanding at the beginning of the period (in shares)					1,884,937
Options outstanding at the end of the period (in shares)					1,656,002
Vesting period (in years)					four-year
Fair value assumptions
Expected volatility (as a percent)						45.00%
Risk-free interest rate (as a percent)						2.54%
Dividend yield (as a percent)						0.62%
Expected term (in years)						6.0
Total unrecognized compensation cost					$ 1,700,000
Period of recognition of unrecognized compensation cost (in years)					3.8