Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts receivable, current	$ 18,110	$ 20,977
Property and equipment, accumulated depreciation	85,351	78,074
Intangible assets, accumulated amortization	$ 19,875	$ 17,135
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	30,717,775	29,867,701
Common stock, shares outstanding	30,029,731	29,232,807
Treasury stock at cost, shares	688,044	634,894