Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Allowance for trade and other receivables	$ 535	$ 405
Accumulated amortization of intangible assets	$ 263,305	$ 199,248
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	47,413,789	47,194,023