Retirement and Employee Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Contribution expense	$ 2,200,000	$ 1,900,000	$ 900,000
Contributions capitalized	2,800,000	3,800,000	4,200,000
Prior service costs				100,000
Net loss				1,700,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in accumulated other comprehensive income (loss)	(8,400,000)	(5,400,000)
Change in accumulated other comprehensive income (loss) after tax	(5,000,000)	(3,300,000)
Employer contributions	11,100,000
Company's expected contribution				13,500,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in accumulated other comprehensive income (loss)	(2,400,000)	(200,000)
Change in accumulated other comprehensive income (loss) after tax	(1,400,000)	(100,000)
Employer contributions	100,000
Company's expected contribution				300,000
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan included in accumulated other comprehensive income (loss)	(36,900,000)	(26,200,000)
Defined benefit plan included in accumulated other comprehensive income (loss) after tax	22,300,000	15,900,000
Defined benefit plan included in accumulated other comprehensive income (loss) after tax	$ (22,300,000)	$ (15,900,000)