Income Taxes (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Effective Tax Reconciliation [Line Items]
Income tax expense at federal statutory rate	$ 36,000,000		$ 27,000,000	$ 74,000,000	$ 52,000,000
U.S. federal statutory income tax rate	35.00%		35.00%	35.00%	35.00%
REIT Income Not Subject to Tax	(15,000,000)		(6,000,000)	(26,000,000)	(12,000,000)
REIT Income Not Subject to Tax (Rate)	(14.30%)		(8.70%)	(12.40%)	(8.10%)
Other Reconciling Items				(2,000,000)	(1,000,000)
Other Reconciling Items (Rate)				(0.70%)	(0.50%)
Effective IncomeTax Continuing Operations Before Discrete Items	21,000,000		21,000,000	46,000,000	39,000,000
Effective Income Tax Rate Continuing Operations Before Discrete Items	20.70%		26.30%	21.90%	26.40%
Tax Credits CBPC for AFMC Exchange	0		(9,000,000)	(19,000,000)	(9,000,000)
Tax Credits CBPC for AFMC Exchange (Rate)	0.00%		(10.90%)	(8.90%)	(6.00%)
EffectiveincomeTaxReconciliation-GainonconsolidationofNZJV				(5,000,000)	0
EffectiveincomeTaxRateReconciliationGainonconsolidationofNZJV				(2.70%)	0.00%
Other Adjustments	(6,000,000)		0	(2,000,000)	0
Other Adjustments (Rate)	(5.90%)		0.00%	(1.00%)	0.00%
Income Tax Expense as reported	15,249,000		12,035,000	19,695,000	30,338,000
Effective tax rate	14.80%		15.40%	9.30%	20.40%
Proceeds from Divestiture of Businesses		$80 million plus a working capital adjustment
Discontinued Operation, Tax Effect of Discontinued Operation	0		1,505,000	22,273,000	1,927,000
Discontinued Operation, Tax Effect of Income (Loss) from Disposal of Discontinued Operation					21,400,000
Interal Asset Transfer Benefit [Member]
Effective Tax Reconciliation [Line Items]
Income Tax Reconciliation, Other Adjustments		$ 4,900,000