Stock-based compensation (Details) (USD $)	1 Months Ended	12 Months Ended
	Jul. 31, 2014	Dec. 26, 2014	Dec. 27, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total after-tax stock based compensation expense		$ 2,479,000	$ 1,914,000
Stock Options Shares [Roll Forward]
Opening stock options outstanding (in shares)		343,000
Ending stock options outstanding as of end of period (in shares)			343,000
Restricted Stock [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total after-tax stock based compensation expense		1,704,000	898,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accelerated vesting awards	300,000
Total unrecognized compensation cost related to restricted stock grants		1,300,000
Unrecognized compensation expected weighted-average recognition period		2 years 10 months 10 days
Restricted Stock and Units activity [Roll Forward]
Opening nonvested at beginning of period (in shares)		300,000	104,000
Granted (in shares)		760,000	284,000
Vested (in shares)		(445,000)	(55,000)
Forfeited/canceled (in shares)		(41,000)	(33,000)
Ending nonvested at end of period (in shares)		574,000	300,000
Restricted Stock and Units - Weighted Average Stock Grant Price [Abstract]
Opening nonvested restricted stock and units (in dollars per share)		$ 8.91	$ 26.92
Granted (in dollars per share)		$ 2.85	$ 3.80
Vested (in dollars per share)		$ 4.18	$ 17.15
Forfeited/canceled (in dollars per share)		$ 4.49	$ 7.82
Ending nonvested restricted stock and units at end of period (in dollars per share)		$ 3.01	$ 8.91
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total after-tax stock based compensation expense		775,000	1,016,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accelerated vesting awards	100,000
Total unrecognized compensation cost related to restricted stock grants		200,000
Unrecognized compensation expected weighted-average recognition period		2 years 2 months 16 days
Weighted average fair value of stock options granted (in dollars per share)		$ 2.73	$ 2.73
Exercise prices of the options outstanding, minimum (in dollars per share)		$ 2.86
Exercise prices of the options outstanding, maximum (in dollars per share)		$ 61.50
Stock Options Shares [Roll Forward]
Opening stock options outstanding (in shares)		343,000	127,000
Granted (in shares)		17,000	253,000
Exercised (in shares)		0	0
Forfeited/canceled (in shares)		(48,000)	(37,000)
Ending stock options outstanding as of end of period (in shares)		312,000	343,000
Ending stock options exercisable (in shares)		227,000	54,000
Stock Options - Weighted Average Option Grant Price [Abstract]
Opening stock options outstanding (in dollars per share)		$ 18.13	$ 45.10
Granted (in dollars per share)		$ 2.86	$ 3.82
Exercised (in dollars per share)		$ 0.00	$ 0.00
Forfeited/canceled (in dollars per share)		$ 7.46	$ 12.69
Ending stock options outstanding (in dollars per share)		$ 18.87	$ 18.13
Ending stock options exercisable (in dollars per share)		$ 24.02	$ 45.44
Stock Options -Aggregate Intrinsic Value [Abstract]
Outstanding as of end of period		0	0
Exercisable at end of period		0	0
Weighted average assumptions based on date of grant [Abstract]
Dividend yield (as a percent)		0.00%	0.00%
Volatility (as a percent)		97.60%	97.60%
Risk-free interest rate (as a percent)		0.80%	0.80%
Expected life (in years)		4 years 9 months 18 days	4 years 9 months 18 days
Selling, General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total after-tax stock based compensation expense		1,304,000	1,914,000
CEO Transition Costs [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total after-tax stock based compensation expense		$ 1,175,000	$ 0