Subsequent Events (Details) (USD $)	0 Months Ended	1 Months Ended	6 Months Ended	12 Months Ended
	Jul. 15, 2013	Jul. 18, 2013	Jun. 30, 2013	Dec. 31, 2012
Subsequent Events (Textuals) [Abstract]
Cash dividend declared per common share	$ 0.30
Repurchase of common stock, shares		28,600	654,277
Weighted-average price per share of common stock repurchased		$ 63.51	$ 61.95
Common share amount available for additional share repurchase		$ 79,600,000	$ 81,400,000	$ 46,900,000
Dividend declared
Subsequent Events (Textuals) [Abstract]
Subsequent event amount	5,700,000
Convertible Notes
Subsequent Events (Textuals) [Abstract]
Conversion rate of common stock shares per $1,000 of principal amount	20.7714		20.7522
Principal amount in conversion feature	$ 1,000		$ 1,000
Conversion price per share of note	$ 48.14		$ 48.19
Call Options
Subsequent Events (Textuals) [Abstract]
Exercise price per share of Call Options	$ 48.14		$ 48.19
Warrants
Subsequent Events (Textuals) [Abstract]
Exercise price per share of Warrants	61.14		61.19