Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Income Per Common Share [Abstract]
Income from continuing operations available to common stockholders									$ 33,130	$ 33,110	$ 73,459
Income from continuing operations available to common stockholders (in shares)									32,541,792	29,667,064	27,269,547
Income from continuing operations available to common stockholders (in dollars per share)									$ 1.02	$ 1.12	$ 2.69
Income from discontinued operations									7,238	654	8,741
Income from discontinued operations (in shares)									32,541,792	29,667,064	27,269,547
Income from discontinued operations (in dollars per share)									$ 0.22	$ 0.02	$ 0.32
Income available to common stockholders	13,937	7,688	10,325	8,418	4,778	6,377	9,482	13,127	40,368	33,764	82,200
Income available to common stockholders (in dollars per share)	$ 0.42	$ 0.23	$ 0.32	$ 0.27	$ 0.16	$ 0.21	$ 0.32	$ 0.45	$ 1.24	$ 1.14	$ 3.01
Effect of Dilutive Securities ( 1 )									0	0	4,224
Effect of Dilutive Securities ( 1 ) (in shares)									33,110	67,319	2,477,067
Income from continuing operations available to common stockholders ( 1 )									33,130	33,110	73,459
Add: noncontrolling interests OP unitholders ( 2 )	0				0				0	0	3,508
Adjusted income from continuing operations available to common stockholders ( 1 )									33,130	33,110	76,967
Adjusted income from continuing operations available to common stockholders ( 1 ) (in shares)									32,628,714	29,734,383	29,746,614
Adjusted income from continuing operations available to common stockholders ( 1 ) (in dollars per share)									$ 1.02	$ 1.11	$ 2.59
Income (loss) from discontinued operations available to common stockholders									7,238	654	8,741
Add: noncontrolling interests OP unitholders ( 2 )	0				0				0	0	716
Adjusted income from discontinued operations available to common stockholders									7,238	654	9,457
Adjusted income from discontinued operations available to common stockholders (in shares)									32,628,714	29,734,383	29,746,614
Adjusted income from discontinued operations available to common stockholders (in dollars per share)									$ 0.22	$ 0.03	$ 0.32
Total income (Diluted)									$ 40,368	$ 33,764	$ 86,424
Total income per common share amount (in dollars per share)	$ 0.42	$ 0.23	$ 0.32	$ 0.27	$ 0.16	$ 0.21	$ 0.32	$ 0.45	$ 1.24	$ 1.14	$ 2.91
Convertible Limited Partnership Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units									2,231,807	2,293,886	2,447,751
Anti-dilutive securities (in shares)									2,231,807	2,293,886	2,447,751
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units									175,500	123,164	260,736
Anti-dilutive securities (in shares)									175,500	123,164	260,736