Noncontrolling Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Redeemable Noncontrolling Interests [Abstract]
Balance - beginning balance	$ 7,700	$ 7,546	$ 7,546
Redemption value adjustment	79	(691)	500
Net (Loss) Income Attributable to Redeemable Noncontrolling Interest	(43)	603
Minority Interest Decrease From Distributions To Redeemable Noncontrolling Interest Holders	(816)	(545)
Foreign Currency Translation Adjustment Attributable To Redeemable Noncontrolling Interests	9	7
Balance - end of period	6,929	6,920	7,700
Statement [Line Items]
Balance - beginning of period	716,402
Redemption value adjustment	79	(691)	500
Windfall tax benefit - share incentive income	4,597	293
Stock-based compensation expense	5,261	2,451
Balance - end of period	717,990		716,402
Parent [Member]
Redeemable Noncontrolling Interests [Abstract]
Redemption value adjustment	(79)	691
Statement [Line Items]
Balance - beginning of period	682,581	625,013	625,013
Shares issued	4,249
Contributions	0	0
Redemption value adjustment	(79)	691
Windfall tax benefit - share incentive income	4,597	293
Stock-based compensation expense	5,261	2,451
Distributions	(23,330)	(20,418)
Shares repurchased	(4,305)	(2,860)
Change in other comprehensive income	2,531	5,764
Net Income Loss Excluding Redeemable Noncontrolling Interest	12,290	23,343
Balance - end of period	683,795	634,277
Noncontrolling Interest [Member]
Redeemable Noncontrolling Interests [Abstract]
Redemption value adjustment	0	0
Statement [Line Items]
Balance - beginning of period	33,821	40,461	40,461
Shares issued	0
Contributions	750	617
Redemption value adjustment	0	0
Windfall tax benefit - share incentive income	0	0
Stock-based compensation expense	0	0
Distributions	(181)	(887)
Shares repurchased	0	0
Change in other comprehensive income	383	911
Net Income Loss Excluding Redeemable Noncontrolling Interest	(578)	(330)
Balance - end of period	34,195	40,772
Total Equity [Member]
Redeemable Noncontrolling Interests [Abstract]
Redemption value adjustment	(79)	691
Statement [Line Items]
Balance - beginning of period	716,402	665,474	665,474
Shares issued	4,249
Contributions	750	617
Redemption value adjustment	(79)	691
Windfall tax benefit - share incentive income	4,597	293
Stock-based compensation expense	5,261	2,451
Distributions	(23,511)	(21,305)
Shares repurchased	(4,305)	(2,860)
Change in other comprehensive income	2,914	6,675
Net Income Loss Excluding Redeemable Noncontrolling Interest	11,712	23,013
Balance - end of period	$ 717,990	$ 675,049