Stockholders' Equity (Details) (USD $)	0 Months Ended					3 Months Ended		6 Months Ended		0 Months Ended
	Jun. 17, 2013	May 23, 2013	May 02, 2013	Dec. 31, 2012	Dec. 20, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Aug. 01, 2013 Subsequent Event [Member]
Class of Stock [Line Items]
Dividend per share			$ 0.19		$ 0.19					$ 0.19
Total cash payments of dividends	$ 2,200,000			$ 2,200,000				$ 2,200,000	$ 3,900,000
Repurchase of common stock, authorized amount of increase		30,000,000.0
Repurchase of common stock, available amount for future share repurchases		2,300,000						32,000,000
Repurchase of common stock, number of shares repurchased						5,502	0	77,609	17,800
Repurchase of common stock, average price per share						$ 57.48		$ 49.56	$ 39.50
Repurchase of common stock, total repurchase costs						$ 300,000	$ 0	$ 3,800,000	$ 700,000