Retirement and Employee Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012
Contribution expense	$ 1,900,000	$ 900,000	$ 800,000
Contributions capitalized	3,800,000	4,200,000	3,300,000
Prior service costs				300,000
Net loss				1,200,000
Transition obligation costs				100,000
Pension Benefits [Member]
Change in accumulated other comprehensive income (loss)	(5,400,000)	(2,400,000)
Change in accumulated other comprehensive income (loss) after tax	(3,300,000)	(1,200,000)
Employer contributions	12,500,000
Company's expected contribution				12,700,000
Other Postretirement Benefits [Member]
Change in accumulated other comprehensive income (loss)	(200,000)	(400,000)
Change in accumulated other comprehensive income (loss) after tax	(100,000)	(200,000)
Employer contributions	100,000
Company's expected contribution				200,000
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Defined benefit plan included in accumulated other comprehensive income (loss)	(26,200,000)	(20,500,000)
Defined benefit plan included in accumulated other comprehensive income (loss) after tax	$ (15,900,000)	$ (12,500,000)