Commitments and Contingencies (Details 2) (Restaurant leaseholds, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 27, 2010	Jan. 02, 2012
Commitments and contingencies
Contractual obligation	$ 2.1	$ 3.6	$ 2.6
Landlord allowances presented as a long-term liability in other liabilities	0.5	0.9	0.7
Minimum
Commitments and contingencies
Renewal option, period	3 years
Maximum
Commitments and contingencies
Renewal option, period	5 years
Terminated operating leases
Commitments and contingencies
Contractual obligation	0.2		0.2
Lease termination charges		0.2
Future minimum lease payments	2.0
Contractual obligation, current	0.01		0.01
Terminated operating leases | Minimum
Commitments and contingencies
Operating lease, remaining term	1 year
Terminated operating leases | Maximum
Commitments and contingencies
Operating lease, remaining term	6 years
Terminated operating leases | Midwest
Commitments and contingencies
Number of restaurant leases terminated		1
Terminated operating leases | Seattle
Commitments and contingencies
Number of restaurant leases terminated		1
Standby letters of credit
Commitments and contingencies
Letters of credit provided as security deposits	$ 0.2