Stockholders' Equity - Change in Ownership of Less-than-wholly-owned Subsidiary (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Net income attributable to common stockholders	$ 18,073	[1]	$ 4,153	[2]	$ 6,011	[3]	$ 3,963	[4]	$ 12,456	[5]	$ 19,783	[6]	$ (24,238)	[7]	$ (1,018)	[8]	$ 32,200	$ 6,983	$ 5,535
Net transfers to the noncontrolling interest																	(8,189)
Change to the Company's total stockholders' equity from net income attributable to common stockholders and transfers to noncontrolling interest																	25,310	6,946	5,465
Cumulative net income attributable to common stockholders [Member]
Noncontrolling Interest [Line Items]
Net income attributable to common stockholders																	31,887	6,946	5,465
Additional Paid-in Capital [Member]
Noncontrolling Interest [Line Items]
Net decrease in the Company's additional paid-in capital for purchase of subsidiary partnership interest																	6,577
Net transfers to the noncontrolling interest																	$ (6,577)

[1] The increases in net income and amounts per share for the fourth quarter of 2014 are primarily attributable to gains on sales of real estate totaling $9.3 million, partially offset by impairment charges of $1.0 million.

[2] The decreases in net income and amounts per share for the third quarter of 2014 are primarily attributable to impairment charges of

[3] The increases in net income and amounts per share for the second quarter of 2014 are primarily attributable to a $1.9 million cash reimbursement received by the Company for certain operating expenses paid by the Company for years 2006 through 2013

[4] The decreases in net income and amounts per share for the first quarter of 2014 are primarily attributable to impairment charges of $3.4 million.

[5] The increases in net income and amounts per share for the fourth quarter of 2013 are primarily attributable to gains on sales of real estate totaling $2.7 million.

[6] The increases in net income and amounts per share for the third quarter of 2013 are primarily attributable to gains on sales of real estate totaling $20.2 million, partially offset by impairment charges of $6.3 million.

[7] The decreases in net income and amounts per share for the second quarter of 2013 are primarily attributable to losses of extinguishment of debt of $29.9 million, of which $0.3 million is included in discontinued operations. This amount is partially offset by gains on sales of real estate totaling $1.8 million.

[8] The decreases in net income and amounts per share for the first quarter of 2013 are primarily attributable to impairment charges of $3.6 million.