Basis of Presentation (Details) Share Based Compensation (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		1 Months Ended				6 Months Ended		12 Months Ended	6 Months Ended
	Jun. 30, 2012 plan	Jun. 30, 2011	Jun. 30, 2012 plan	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 RSU	Jun. 30, 2011 RSU	Jun. 30, 2012 RSU	Jun. 30, 2011 RSU	May 31, 2011 RSA	May 31, 2010 RSA	May 31, 2009 RSA	May 31, 2008 RSA	Jun. 30, 2012 RSA	Jun. 30, 2012 SAR	Dec. 31, 2011 SAR	Jun. 30, 2012 Common Stock	Jun. 30, 2012 Common Stock RSU
Share-based Compensation
Number of stock-based compensation plans in effect	1		1
Number of shares of issuable common shares	2,654,000		2,654,000
Stock-based compensation expense						$ 896,000	$ 1,100,000	$ 1,900,000	$ 2,200,000
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
Granted								13,716
Vested								(140,000)						(5,046)
Outstanding, end of period						467,716		467,716						0	1,812,079	1,812,079
Unrecognized compensation cost						8,403,000		8,403,000						0
Summary of SAR Activity, Other Data:
Outstanding, weighted average contractual term															4 years	4 years 6 months
Weighted average exercise price, outstanding															$ 36.16
Outstanding, weighted average contractual term															4 years	4 years 6 months
Weighted average exercise price, outstanding															$ 36.16	$ 36.16
Deferred Compensation:
Deferred compensation payable	37,957,000		37,957,000		36,315,000
Increase in deferred compensation liability			1,700,000
Increase in fair value of plan assets			1,500,000
Deferred compensation expense	$ (127,000)	$ 1,100,000	$ 1,500,000	$ 2,200,000