Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Condensed Consolidated Balance Sheets
Accounts receivable, accumulated provision for doubtful accounts (in dollars)	$ 14,696	$ 12,586
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, authorized shares	320,000	320,000
Common stock, shares issued	175,684	175,684
Treasury stock, shares	25,249	25,575