CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Billed receivables, allowances	$ 8,834	$ 8,117
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued
Preferred stock, shares outstanding
Common stock, par value	$ 0.005	$ 0.005
Common stock, shares authorized	70,000,000	70,000,000
Common stock, shares issued	46,606,796	46,606,796
Treasury stock, shares	6,769,149	7,159,023