Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts receivable, current	$ 18,607	$ 17,438
Property and equipment, accumulated depreciation	101,941	94,266
Intangible assets, accumulated amortization	$ 21,314	$ 20,611
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common Stock, par value	$ 0.001	$ 0.001
Common Stock, shares authorized	60,000,000	60,000,000
Common Stock, shares issued	31,443,152	31,017,363
Common Stock, shares outstanding	30,730,529	30,328,549
Treasury Stock at cost, shares	712,623	688,814