Earnings per Share and Unit (Details) (USD $) In Thousands, except Share data, 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
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Document Fiscal Year Focus									2014
Current Fiscal Year End Date									--12-31
Weighted Average Limited Partnership Units Outstanding, Basic									157,950	171,886	177,164
Numerator [Abstract]
Net income (loss) attributable to common stockholders	$ 73,515	$ 47,942	$ 25,482	$ 19,389	$ 46,326	$ 34,998	$ 31,864	$ 15,554
Income (loss) per common share - basic (note 15):
Net income attributable to common stockholders (in dollars per share)	$ 0.79	$ 0.52	$ 0.28	$ 0.21	$ 0.50	$ 0.38	$ 0.35	$ 0.17
Income (loss) per common share - diluted (note 15):
Net income (loss) attributable to common stockholders (in dollars per share)	$ 0.79	$ 0.52	$ 0.28	$ 0.21	$ 0.50	$ 0.38	$ 0.35	$ 0.17
Parent Company [Member]
Numerator [Abstract]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest									0	121	(43)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0	65,164	(21,685)
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest									1,457	1,360	385
Income (Loss) from Continuing Operations Attributable to Parent									187,390	84,640	47,552
Less: preferred stock dividends									21,062	21,062	32,531
Net income attributable to noncontrolling interests									1,457	1,481	342
Net income (loss) attributable to common stockholders									165,875	128,294	(7,236)
Less: dividends paid on unvested restricted stock									453	448	572
Add: dividends paid on Treasury Method restricted stock									63	45	71
Net (loss) income for common stockholders - diluted									165,938	128,339	(7,165)
Denominator [Abstract]
Weighted average common shares/units outstanding for basic EPS/EPU									92,370,000	91,383,000	89,630,000
Incremental Common Shares Attributable to Dilutive Effect of Call Options and Warrants									0	2,000	0
Incremental shares to be issued under unvested restricted stock									34,000	24,000	39,000
Weighted average common shares/units outstanding for diluted EPS/EPU									92,404,000	91,409,000	89,669,000
Income (loss) per common share - basic (note 15):
Continuing operations (in dollars per share)									1.80	0.69	0.16
Discontinued operations (in dollars per share)									0.00	0.71	(0.24)
Net income attributable to common stockholders (in dollars per share)									1.80	1.40	(0.08)
Income (loss) per common share - diluted (note 15):
Continuing operations (in dollars per share)									1.80	0.69	0.16
Discontinued operations (in dollars per share)									0.00	0.71	(0.24)
Net income (loss) attributable to common stockholders (in dollars per share)									1.80	1.40	(0.08)
Earnings Per Common Unit - Diluted [Abstract]
Income from continuing operations									133,770	84,297	45,779
Partnership Interest [Member]
Numerator [Abstract]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest									0	121	(43)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0	65,164	(21,685)
Income (Loss) from Continuing Operations Attributable to Parent									187,709	84,916	47,029
Less: preferred unit distributions									21,062	21,062	31,902
Net income attributable to noncontrolling interests									1,138	1,205	865
Net income (loss) attributable to common stockholders									166,194	128,570	(7,130)
Net (loss) income attributable to common unit holders									166,647	129,018	(6,558)
Less: dividends paid on unvested restricted stock									453	448	572
Add: dividends paid on Treasury Method restricted stock									63	45	71
Net (loss) income for common stockholders - diluted									166,257	128,615	(7,059)
Denominator [Abstract]
Weighted average common shares/units outstanding for basic EPS/EPU									92,528,000	91,555,000	89,808,000
Incremental Common Shares Attributable to Dilutive Effect of Call Options and Warrants									0	2,000	0
Incremental shares to be issued under unvested restricted stock									34,000	24,000	39,000
Weighted average common shares/units outstanding for diluted EPS/EPU									92,562,000	91,581,000	89,847,000
Earnings Per Common Unit, Basic [Abstract]
Continuing operations (in dollars per share)									1.80	0.69	0.16
Discontinued operations (in dollars per share)									0.00	0.71	(0.24)
Net income attributable to common unit holders (in dollars per share)									1.80	1.40	(0.08)
Earnings Per Common Unit - Diluted [Abstract]
Continuing operations (in dollars per share)									1.80	0.69	0.16
Discontinued operations (in dollars per share)									0.00	0.71	(0.24)
Net Income (Loss), Net of Tax, Per Outstanding Limited Partnership Unit, Diluted									1.80	1.40	(0.08)
Income from continuing operations									133,770	84,297	45,779
Continuing operations | Parent Company [Member]
Numerator [Abstract]
Net income (loss) attributable to common stockholders									165,875	63,130	14,449
Net (loss) income for common stockholders - diluted									165,938	63,175	14,520
Continuing operations | Partnership Interest [Member]
Numerator [Abstract]
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest									1,138	1,084	908
Net income (loss) attributable to common stockholders									166,194	63,406	14,555
Net (loss) income for common stockholders - diluted									166,257	63,451	14,626