Share Based Compensation, 401(k) Plan and Deferred Compensation (Details Textuals) (USD $)	12 Months Ended				1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Mar. 31, 2011 Stock Option [Member] Age	Dec. 31, 2011 Stock Option [Member] Years	Dec. 31, 2010 Stock Option [Member]	Dec. 31, 2009 Stock Option [Member]	Mar. 31, 2011 Restricted Share Awards [Member] Age	Dec. 31, 2011 Restricted Share Awards [Member] Years	Dec. 31, 2010 Restricted Share Awards [Member]	Dec. 31, 2009 Restricted Share Awards [Member]	Mar. 31, 2011 Restricted Performance Share Units Plan [Member] Age	Dec. 31, 2011 Restricted Performance Share Units Plan [Member]	Dec. 31, 2010 Restricted Performance Share Units Plan [Member]	Dec. 31, 2009 Restricted Performance Share Units Plan [Member]	Apr. 02, 2009 Restricted Performance Share Units Plan [Member]	Dec. 31, 2011 Outperformance Program [Member]	Dec. 31, 2010 Outperformance Program [Member]	Dec. 31, 2009 Outperformance Program [Member]	Dec. 31, 2011 Employee Share Purchase Plan [Member]	Dec. 31, 2010 Employee Share Purchase Plan [Member]	Dec. 31, 2009 Employee Share Purchase Plan [Member]	Dec. 31, 2011 Deferred Compensation Plan [Member]	Dec. 31, 2010 Deferred Compensation Plan [Member]	Dec. 31, 2009 Deferred Compensation Plan [Member]	May 24, 2011 Executive Officer [Member] Stock Option [Member]	Mar. 02, 2011 Executive Officer [Member] Stock Option [Member]	Mar. 02, 2011 Executive Officer [Member] Restricted Share Awards [Member]	Mar. 02, 2011 Executive Officer [Member] Restricted Performance Share Units Plan [Member]	Mar. 04, 2010 Executive Officer [Member] Restricted Performance Share Units Plan [Member]	Apr. 01, 2009 Executive Officer [Member] Restricted Performance Share Units Plan [Member]
Share Based and Deferred Compensation (Textuals) [Abstract]
Options outstanding under equity incentive plan	3,599,672	3,116,611	2,404,567	1,754,648
Unvested options						1,311,943
Unrecognized compensation expenses						$ 2,400,000				$ 3,700,000
Weighted average period over which options will be recognized						1.5				1.1
Compensation expense recognized	6,400,000	6,100,000	5,300,000			1,400,000	1,000,000	600,000		3,200,000	4,000,000	3,200,000		1,700,000	1,000,000	400,000		100,000	400,000	900,000	100,000	200,000	300,000
Restricted shares outstanding										807,291	851,278
Vesting Period, Minimum										3 Years
Vesting Period, Maximum										7 Years
Stock-based compensation expense, capitalized	1,500,000	1,300,000	800,000			400,000				700,000	900,000	800,000		500,000
Recognized compensation expense awards nominal amounts capitalized																0
Aggregate share-based awards awarded to executives																					1,250,000						101,437	603,241	174,012	124,293	120,955	488,292
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period						3 years			3 years	three to seven years from the initial grant date				3 years				5 years
Share-based Compensation Arrangement by Share-based Payment Award, Cliff Vesting, Minimum										3 years
Share-based Compensation Arrangement by Share-based Payment Award, Term	10 years
Voluntary termination of employment terms					after reaching age 57 and accumulating at least 15 years years of service with the Company				after reaching age 57 and accumulating at least 15 years years of service with the Company				after reaching age 57 and accumulating at least 15 years years of service with the Company
Age limit of voluntary termination of employment					57				57				57
Accumulated Service Period For Voluntary Termination					15 years				15 years				15 years
Maximum number of shares to be delivered at the end of the measurement period relative to the total shareholder return														equal a certain percentage (not to exceed 200%) of the participant's base units
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Delivered																	372,101
Maximum percentage of the participant's base units														200.00%
Fair value of awards on the grant date														2,000,000	2,000,000	1,100,000		5,900,000
Share purchases made by employees under ESPP																					85% of the average closing price per share for a specified period
Share purchases made by employees under ESPP, Percentage																					85.00%
Percentage of plan contribution																					20.00%
Amount of participant contribution																					50,000
Purchase price of shares purchased under ESPP																					$ 400,000	$ 500,000	$ 400,000
Number of shares to be issued under deferred compensation plan included in total shares outstanding																								300,000	300,000
Deferred Compensation Arrangement With Individual Increase In Compensation Expense																								100,000	1,000,000	1,500,000
Deferred Compensation Arrangement With Individual Decrease In Compensation Expense																									$ 1,000,000	$ 1,800,000