Stock Repurchase Program (Details) (USD $) Share data in Thousands, unless otherwise specified	3 Months Ended		0 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 08, 2012 2011 Stock Repurchase Program [Member]	May 02, 2011 2011 Stock Repurchase Program [Member]	Mar. 31, 2013 2011 Stock Repurchase Program [Member]	Dec. 31, 2012 2011 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount			$ 323,700,000	$ 300,000,000
Treasury stock shares acquired					2,700
Treasury stock value acquired cost method	85,215,000	19,238,000			70,000,000
Stock repurchase program remaining authorized repurchase amount					$ 280,000,000	$ 350,000,000