Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowances for doubtful accounts	$ 5,102	$ 3,258
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	44,957,890	43,748,237
Common stock, shares outstanding	41,858,697	40,673,042
Treasury stock, shares	3,099,193	3,075,195