Stockholders' Equity - Change in Ownership of Less-than-wholly-owned Subsidiary (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[2]	Jun. 30, 2015	[3]	Mar. 31, 2015	[4]	Dec. 31, 2014	[5]	Sep. 30, 2014	[6]	Jun. 30, 2014	[7]	Mar. 31, 2014	[8]	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Noncontrolling Interest [Line Items]
Net income attributable to common stockholders	$ 18,658		$ 27,480		$ 17,916		$ 5,382		$ 18,073		$ 4,153		$ 6,011		$ 3,963		$ 69,436	$ 32,200	$ 6,983
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																	69,436	25,310	6,946
Cumulative net income attributable to common stockholders [Member]
Noncontrolling Interest [Line Items]
Net income attributable to common stockholders																	69,436	31,887	$ 6,946
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																	$ 0	(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 2015 are primarily attributable to gains on sales of real estate totaling $9.1 million, partially offset by impairment charges of $0.7 million.

[2] The increases in net income and amounts per share for the third quarter of 2015 are primarily attributable to a $10.6 million gain on the sale of one property previously classified as an asset held for sale.

[3] The increases in net income and amounts per share for the second quarter of 2015 are primarily attributable to a $41.5 million gain on the sale of two properties, partially offset by a $28.0 million loss on extinguishment of the Senior Notes due 2017.

[4] The decreases in net income and amounts per share for the first quarter of 2015 are primarily attributable to impairment charges of $3.3 million

[5] 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.

[6] The decreases in net income and amounts per share for the third quarter of 2014 are primarily attributable to impairment charges of $4.5 million.

[7] 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.

[8] 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.