Stock-Based Compensation Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified		9 Months Ended		12 Months Ended					64 Months Ended	12 Months Ended
	May 24, 2007	Sep. 30, 2012 1996 Stock Options/Stock Issuance Plan	Sep. 30, 2012 Restricted stock The 2007 plan	Dec. 31, 2012 Restricted stock The 2007 plan item	Dec. 31, 2011 Restricted stock The 2007 plan item	Dec. 31, 2010 Restricted stock The 2007 plan item	Dec. 31, 2009 Restricted stock The 2007 plan item	Dec. 31, 2008 Restricted stock The 2007 plan	Sep. 30, 2012 Restricted stock The 2007 plan	Dec. 31, 2012 Restricted stock vesting over 4 years The 2007 plan	Dec. 31, 2011 Restricted stock vesting over 4 years The 2007 plan	Dec. 31, 2010 Restricted stock vesting over 4 years The 2007 plan	Dec. 31, 2009 Restricted stock vesting over 4 years The 2007 plan	Dec. 31, 2012 Restricted stock vesting on the first anniversary date from date of issuance The 2007 plan	Dec. 31, 2011 Restricted stock vesting on the first anniversary date from date of issuance The 2007 plan	Dec. 31, 2010 Restricted stock vesting on the first anniversary date from date of issuance The 2007 plan	Dec. 31, 2009 Restricted stock vesting on the first anniversary date from date of issuance The 2007 plan
Stock-based compensation plans
Number of shares authorized	2,000,000
Awards granted (in shares)									1,616,156	171,000	324,924	190,375	10,000	28,040	22,100	21,635	18,220
Number of types of awards granted				2	2	2	2
Vesting period										4 years	4 years	4 years	4 years	1 year	1 year	1 year	1 year
Awards canceled (in shares)				8,988	27,477			33,043
Stock compensation expense (in dollars)			$ 2.3
Remaining average vesting period for recognition of unrecognized compensation expense			2 years 3 months 18 days
Unrecognized compensation expense (in dollars)			6.5						6.5
Intrinsic value of unvested awards (in dollars)			7.8						7.8
Stock options exercised (in shares)		232,314
Stock options outstanding (in shares)		211,267
Intrinsic value of outstanding stock options (in dollars)		$ 0.9