Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings per Share
Income from continuing operations	$ 13,143	$ 12,361	$ 26,090	$ 24,634
Less net income allocated to non-controlling interests	(10)	(48)	(21)	(96)
Less net income allocated to participating securities:
Nonforfeitable dividends on participating securities	(91)	(85)	(185)	(174)
Total net income allocated to participating securities	(91)	(85)	(185)	(174)
Less net income allocated to preferred stockholders:
Preferred stock dividends	(818)	(818)	(1,636)	(3,876)
Preferred stock redemption charge				(3,566)
Total net income allocated to preferred stockholders	(818)	(818)	(1,636)	(7,442)
Income from continuing operations available to common stockholders	12,224	11,410	24,248	16,922
Discontinued operations:
Loss from discontinued operations	(30)	(99)	(61)	(218)
Gain on sale of assets, net			16
Net loss from discontinued operations	(30)	(99)	(45)	(218)
Net income available to common stockholders	12,194	11,311	24,203	16,704
Net income for diluted net income per share	$ 12,194	$ 11,311	$ 24,203	$ 16,704
Shares for basic net income per share	30,213	30,135	30,201	28,233
Effect of dilutive securities:
Stock options (in shares)	45	33	45	31
Shares for diluted net income per share	30,258	30,168	30,246	28,264
Basic net income per share	$ 0.40	$ 0.38	$ 0.80	$ 0.59
Diluted net income per share	$ 0.40	$ 0.37	$ 0.80	$ 0.59