Basis of Presentation (Details) Share Based Compensation (USD $)	3 Months Ended			3 Months Ended		1 Months Ended				3 Months Ended		12 Months Ended	3 Months Ended
	Mar. 31, 2012 plan	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 RSU	Mar. 31, 2011 RSU	May 31, 2011 RSA	May 31, 2010 RSA	May 31, 2009 RSA	May 31, 2008 RSA	Mar. 31, 2012 RSA	Mar. 31, 2012 SAR	Dec. 31, 2011 SAR	Mar. 31, 2012 Common Stock	Mar. 31, 2012 Common Stock RSU
Share-based Compensation
Number of stock-based compensation plans in effect	1
Number of shares of issuable common shares	2,654,000
Stock-based compensation expense				$ 1,000,000	$ 1,100,000
Exercise of restricted stock unit, shares													94,000	94,176
RSA issued to each non-employee director						700	700	700	700
Summary of Activity of the RSU, RSA and SAR:
Outstanding, beginning of period				594,000						5,046	1,812,079
Vested				(140,000)						(146)
Outstanding, end of period				454,000						4,900	1,812,079	1,812,079
Unrecognized compensation cost				8,999,000						24,000
Summary of SAR Activity, Other Data:
Outstanding, weighted average remaining contractual term											4 years	4 years 6 months
Weighted average fair value, outstanding											$ 36.16
Outstanding, weighted average remaining contractual term											4 years	4 years 6 months
Weighted average fair value, outstanding											$ 36.16	$ 36.16
Deferred Compensation:
Deferred compensation payable	38,086,000		36,315,000
Increase in deferred compensation liability	1,800,000
Increase in fair value of plan assets	1,600,000
Deferred compensation expense	$ 1,600,000	$ 1,200,000