Comprehensive Income and Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, 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
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Net income	$ 12,850	$ 8,244	$ 14,434	$ 12,443	$ 11,399	$ 8,773	$ 40,049	$ 12,082	$ 47,971	$ 72,303	$ 61,694
Other comprehensive income/(loss):
Unrealized gain/(loss) on tax increment financing bond									234	(177)	293
Unrealized gains/(losses) on cash flow hedges									(2,202)	0	937
Amortization of settled cash flow hedges									(118)	237	(249)
Sale of cash flow hedge related to disposition of investment in unconsolidated affiliate									0	103	0
Total other comprehensive income/(loss)									(2,086)	163	981
Total comprehensive income									45,885	72,466	62,675
Components of AOCL
Tax increment financing bond	(2,308)				(2,543)				(2,308)	(2,543)
Settled and outstanding cash flow hedges	(3,426)				(1,105)				(3,426)	(1,105)
Total accumulated other comprehensive loss	$ (5,734)				$ (3,648)				$ (5,734)	$ (3,648)