Debt Secured Mortgage Notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Noncash or Part Noncash Acquisition, Debt Assumed	$ 0		$ 105,000,000		$ 0
Carrying value of debt	1,270,052,000		847,339,000
Secured Mortgage Notes Assumed with Timberland Acquisition [Member]
Debt Instrument [Line Items]
Noncash or Part Noncash Acquisition, Debt Assumed, Date	November 2011
Debt Instrument, Collateral	approximately 250,000 acres of timberlands
Noncash or Part Noncash Acquisition, Debt Assumed	0		105,000,000		0
Debt Instrument, Interest Rate, Stated Percentage	4.35%
Debt Instrument, Term	seven years
Debt Instrument, Maturity Date, Description	August 2017
Repayments of Secured Debt	10,500,000		21,000,000
Carrying value of debt	76,731,000	[1]	88,582,000	[1]
Debt Instrument, Outstanding Principal	$ 73,500,000

[1] The mortgage notes due in 2017 were recorded at a premium of $3.2 million and $4.6 million as of December 31, 2012 and 2011, respectively. Upon maturity the liability will be $73.5 million.