Stockholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended		12 Months Ended
	May 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Stockholders' equity
Cost of shares acquired by the entity		$ 0.7	$ 5.1
Authorized shares of common stock		100,000,000
Voting rights per common share		1
Common stock, outstanding shares		16,160,000		15,915,000
Shares acquired by the entity		21,000	214,000
2013 Stock Purchase Plan
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan	$ 10
Period over which repurchases allowed under the plan	12 months
Common stock purchased under the stock purchase plan (in shares)		0
2012 Stock Purchase Plan
Stockholders' equity
Preceding period in which repurchases were allowed under the plan	12 months
Common stock purchased under the stock purchase plan (in shares)		0	1,200,000	4,100,000