Subsequent Events (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 19, 2013	Mar. 31, 2013	Dec. 31, 2012	Apr. 15, 2013
Subsequent Events (Textuals) [Abstract]
Cash dividend declared per common share	$ 0.30
Conversion price per share of note		$ 48.24		$ 48.19
Stock repurchase program, authorized amount by Board of Directors	$ 75,000,000
Repurchase of common stock, shares	210,835	259,596
Weighted-average price per share of common stock repurchased	$ 60.94	$ 62.62
Common share amount available for additional share repurchase	92,800,000	30,700,000	46,900,000
Dividend declared
Subsequent Events (Textuals) [Abstract]
Subsequent event amount	5,800,000
Convertible Notes
Subsequent Events (Textuals) [Abstract]
Conversion rate of common stock shares per $1,000 of principal amount	20.7522	20.7309
Principal amount in conversion feature		$ 1,000		$ 1,000
Call Options
Subsequent Events (Textuals) [Abstract]
Exercise price per share of call options		$ 48.24		$ 48.19
Warrants
Subsequent Events (Textuals) [Abstract]
Exercise price per share of Warrants		61.25		61.19