Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts receivable, current	$ 17,438	$ 20,977
Property and equipment, accumulated depreciation	94,266	78,074
Intangible assets, accumulated amortization	$ 20,611	$ 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	31,017,363	29,867,701
Common stock, shares outstanding	30,328,549	29,232,807
Treasury stock at cost, shares	688,814	634,894