CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts receivable, allowance	$ 10,821	$ 10,439
Accumulated amortization	$ 483,840	$ 469,534
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000	475,000
Common stock, shares issued	83,541	62,178
Common stock shares, outstanding	83,449	62,086
Treasury stock, shares	92	92