Stockholders' Equity (Details) (USD $)	0 Months Ended							1 Months Ended	3 Months Ended	9 Months Ended		0 Months Ended
	Sep. 16, 2013	Aug. 01, 2013	Jun. 17, 2013	May 02, 2013	Apr. 30, 2013	Dec. 31, 2012	Dec. 20, 2012	May 31, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Nov. 02, 2013 Subsequent Event [Member]
Class of Stock [Line Items]
Dividend per share		$ 0.19		$ 0.19			$ 0.19					$ 0.22
Total cash payments of dividends	$ 2,200,000		$ 2,200,000			$ 2,200,000				$ 4,500,000	$ 5,900,000
Repurchase of common stock, authorized amount of increase								30,000,000
Repurchase of common stock, available amount for future share repurchases					2,300,000					30,100,000
Repurchase of common stock, number of shares repurchased									29,031	106,640	17,800
Repurchase of common stock, average price per share									$ 64.45	$ 53.62	$ 39.50
Repurchase of common stock, total repurchase costs									$ 1,900,000	$ 5,700,000	$ 700,000