Share Based and Deferred Compensation (Details Textuals) (USD $)	3 Months Ended		9 Months Ended									1 Months Ended	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended			1 Months Ended	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Mar. 02, 2011 Executive Officer [Member] Restricted Share Awards [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 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]	Mar. 31, 2011 Stock Option [Member] Age	Sep. 30, 2011 Stock Option [Member]	Sep. 30, 2010 Stock Option [Member]	Sep. 30, 2011 Stock Option [Member] Year	Sep. 30, 2010 Stock Option [Member]	Mar. 31, 2011 Restricted Share Awards [Member] Age	Sep. 30, 2011 Restricted Share Awards [Member]	Sep. 30, 2010 Restricted Share Awards [Member]	Sep. 30, 2011 Restricted Share Awards [Member] Year	Sep. 30, 2010 Restricted Share Awards [Member]	Dec. 31, 2010 Restricted Share Awards [Member]	Mar. 31, 2011 Restricted Performance Share Units Plan [Member] Age	Sep. 30, 2011 Restricted Performance Share Units Plan [Member]	Sep. 30, 2010 Restricted Performance Share Units Plan [Member]	Sep. 30, 2011 Restricted Performance Share Units Plan [Member]	Sep. 30, 2010 Restricted Performance Share Units Plan [Member]	Sep. 30, 2009 Restricted Performance Share Units Plan [Member]	Sep. 30, 2011 Outperformance Program [Member]	Sep. 30, 2010 Outperformance Program [Member]	Sep. 30, 2011 Outperformance Program [Member]	Sep. 30, 2010 Outperformance Program [Member]	Sep. 30, 2011 Employee Share Purchase Plan [Member]	Sep. 30, 2010 Employee Share Purchase Plan [Member]	Sep. 30, 2011 Employee Share Purchase Plan [Member]	Sep. 30, 2010 Employee Share Purchase Plan [Member]	Sep. 30, 2011 Deferred Compensation Plan [Member]	Sep. 30, 2010 Deferred Compensation Plan [Member]
Share Based and Deferred Compensation (Textuals) [Abstract]
Options outstanding under equity incentive plan	3,599,673		3,599,673		3,116,611								3,599,673		3,599,673
Unvested options													1,311,943		1,311,943
Unrecognized compensation expenses													$ 2,700,000		$ 2,700,000			$ 4,400,000		$ 4,400,000
Weighted average period over which options will be recognized															1.7					1.4
Compensation expense recognized	1,600,000	1,700,000	4,900,000	4,800,000									400,000	300,000	1,100,000	700,000		800,000	900,000	2,400,000	2,700,000			500,000	300,000	1,200,000	700,000		100,000	100,000	100,000	300,000	100,000	100,000	100,000	100,000
Restricted shares outstanding																		808,098		808,098		851,278
Vesting Period															over three years		after three years from the grant date			three to seven years from initial grant date						Three year
Vesting Period, Minimum																	P3Y			3 Years
Vesting Period, Maximum																				7 Years
Share-based Compensation Arrangement by Share-based Payment Award, Award Expiration Dating			10 Years
Employee Service Share-based Compensation, Capitalized Amount	400,000	400,000	1,100,000	1,000,000									100,000		300,000			200,000	200,000	500,000	700,000			100,000		300,000
Aggregate share-based awards awarded to executives						174,012	101,437	603,241	124,293	120,955	488,292																						1,250,000		1,250,000
Voluntary termination of employment terms												after reaching age 57 and accumulating at least 15 years of service with the Company					after reaching age 57 and accumulating at least 15 years of service with the Company						After reaching age 57 and accumulating at least 15 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
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
Amount of participant contribution																																			50,000
Percentage of plan contribution																																			20.00%
Maximum participant contribution under 2011 plan																																			limited to the lesser of 20% of compensation or $50,000
Purchase price of shares purchased under ESPP																																	$ 100,000	$ 100,000	$ 300,000	$ 400,000
Deferred compensation arrangement with individual increase in compensation expense																																					800,000	800,000
Deferred compensation arrangement with individual decrease in compensation expense																																					$ 400,000	$ 400,000
Number of shares to be issued under deferred compensation plan included in total shares outstanding																																					300,000	300,000