Credit Arrangements (Details)	0 Months Ended	6 Months Ended				0 Months Ended	6 Months Ended		12 Months Ended	6 Months Ended						6 Months Ended				6 Months Ended		6 Months Ended
	Dec. 28, 2012 Senior Notes USD ($)	Jun. 30, 2013 Senior Notes USD ($)	Jun. 30, 2013 Senior Notes Minimum USD ($)	Jun. 30, 2013 Notes Agreement	Jun. 30, 2013 Notes Agreement Minimum	Dec. 28, 2012 Notes Agreement Maximum USD ($)	Jun. 30, 2013 Notes Agreement Maximum	Dec. 18, 2009 Subordinated Promissory Note JCG USD ($)	Dec. 31, 2012 Note A Rockford USD ($)	Jun. 30, 2013 Credit Agreement LIBOR	Jun. 30, 2013 Credit Agreement Base rate	Jun. 30, 2013 Credit Agreement Federal funds rate	Jun. 30, 2013 Credit Agreement Prime rate	Jun. 30, 2013 Credit Agreement Minimum	Jun. 30, 2013 Credit Agreement Revolving line of credit USD ($)	Jun. 30, 2013 Credit Agreement Revolving line of credit Minimum USD ($)	Jun. 30, 2013 Credit Agreement Commercial letters of credit USD ($)	Dec. 31, 2012 Credit Agreement Commercial letters of credit USD ($)	Dec. 31, 2010 Canadian Credit Facility Rockford USD ($)	Jun. 30, 2013 Canadian Credit Facility Commercial letters of credit CAD	Dec. 31, 2012 Canadian Credit Facility Commercial letters of credit CAD	Jun. 30, 2013 Canadian Credit Facility Commercial letters of credit Maximum	Oct. 29, 2009 Agreement with Private Bank and Trust Company USD ($)
Credit arrangements
Maximum borrowing capacity															$ 75,000,000					10,000,000
Incremental maximum borrowing capacity															50,000,000
Variable rate basis										LIBOR	Base Rate	Federal Funds Rate	prime rate
Basis spread on variable rate (as a percent)												0.50%
Prepayment to be paid on debt			5,000,000													5,000,000
Additional borrowings	50,000,000
Interest rate (as a percent)		3.65%
Additional borrowings to be incurred during the first three years of the debt agreement						25,000,000
Number of years in which additional notes can be issued				3 years
Maturity term of debt instrument							10 years
Restrictions on investments, change of control provisions and provisions as a percentage of total assets to be disposed off					20.00%									20.00%
Total commercial letters of credit outstanding																	5,659,000	4,808,000		3,539,000	1,364,000
Available borrowing capacity															69,341,000					6,461,000
Borrowings outstanding															0								0
Term of credit facility																						5 years
Annual fee (as a percent)																				1.00%
Required principal payment		7,100,000
Initial principal amount								53,500,000											16,712,000
Amount outstanding									5,000,000
Payment that the entity was required to make to cancel the notes									$ 1,500,000