Supplemental Selected Quarterly Financial Information (Schedule Of Supplemental Selected Quarterly Financial Information) (Details) (USD $)	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
Total revenues	$ 174,182,000		$ 165,059,000		$ 147,294,000		$ 138,041,000		$ 134,749,000		$ 136,605,000		$ 132,948,000		$ 127,776,000		$ 624,576,000		$ 532,078,000		$ 493,353,000
Gross profit	55,759,000	[1]	54,831,000	[1]	48,963,000	[1]	44,908,000	[1]	43,608,000	[2]	45,154,000	[2]	43,220,000	[2]	39,704,000	[2]	204,461,000	[1]	171,686,000	[2]	148,879,000
Net income	8,046,000	[3]	46,800,000	[3]	8,742,000	[3]	6,558,000	[3]	8,000,000	[4]	20,655,000	[4]	8,248,000	[4]	4,230,000	[4]	70,146,000	[3]	41,133,000	[4]	5,771,000
Net income attributable to controlling interests and available to common stockholders	8,153,000	[3]	46,885,000	[3]	8,715,000	[3]	6,480,000	[3]	8,028,000	[4]	20,763,000	[4]	8,203,000	[4]	3,965,000	[4]	70,233,000	[3]	40,959,000	[4]	5,277,000
Basic net income per common share	$ 0.18	[3]	$ 1.06	[3]	$ 0.20	[3]	$ 0.15	[3]	$ 0.19	[4]	$ 0.49	[4]	$ 0.20	[4]	$ 0.10	[4]	$ 1.60	[3]	$ 0.98	[4]	$ 0.13
Diluted net income per common share	$ 0.18	[3]	$ 1.05	[3]	$ 0.20	[3]	$ 0.15	[3]	$ 0.19	[4]	$ 0.49	[4]	$ 0.19	[4]	$ 0.09	[4]	$ 1.58	[3]	$ 0.96	[4]	$ 0.13
Depreciation, accretion, and amortization expense	16,900,000		15,500,000		13,500,000		13,400,000		13,600,000		13,000,000		12,100,000		12,300,000		59,278,000		50,992,000		51,511,000
Tax benefit																	(13,176,000)		(17,139,000)		4,245,000
Valuation allowance related to United States segments																	1,195,000		(23,624,000)		(994,000)
Pre-tax charges related to refinancing debt											14,500,000
Parent [Member]
Net income																	70,125,000		41,112,000		5,750,000
Net income attributable to controlling interests and available to common stockholders																	70,125,000		41,112,000		5,750,000
Tax benefit																	(12,116,000)		(16,468,000)		4,154,000
U.S. [Member]
Total revenues																	501,439,000		423,109,000		401,934,000
Tax benefit																	(13,176,000)		(17,139,000)		4,245,000
Valuation allowance related to United States segments									$ 3,500,000		$ 23,700,000

[1] Excludes $13.4 million, $13.5 million, $15.5 million and $16.9 million of depreciation, accretion, and amortization for the quarters ended March 31, June 30, September 30, and December 31, respectively.

[2] Excludes $12.3 million, $12.1 million, $13.0 million and $13.6 million of depreciation, accretion, and amortization for the quarters ended March 31, June 30, September 30, and December 31, respectively.

[3] Includes $37.0 million of tax benefit recorded in the quarter ended September 30 as a result of a tax reporting change with respect to the Company's U.K. operations.

[4] Includes release of $23.7 million and $3.5 million in previously-recognized valuation allowances related to the Company's United States segment for the quarters ended September 30 and December 31, respectively. Additionally, the quarter ended September 30 includes pre-tax charges of approximately $14.5 million related to certain charges associated with the refinancing of the Company's outstanding debt obligations.