Stock Repurchase Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	6 Months Ended	1 Months Ended
	Jul. 31, 2013	Jun. 30, 2013	Dec. 31, 2012 Maximum
Stock Repurchase Plan
Authorized amount to repurchase outstanding common stock	$ 150		$ 50
Aggregate shares repurchased		1,573,588
Total cost of shares repurchased		$ 50