Condensed Consolidating Balance Sheet (Details) - USD ($)	Sep. 25, 2016	Dec. 27, 2015	Sep. 27, 2015	Dec. 28, 2014	May 31, 2014
Condensed Financial Statements, Captions [Line Items]
Principal	$ 452,000,000	$ 452,700,000
Current assets:
Cash and cash equivalents	20,500,000	28,500,000	$ 35,800,000	$ 33,500,000
Accounts receivable, net	208,000,000	206,800,000
Amounts due from affiliated companies	0	0
Inventoried costs	58,500,000	55,600,000
Other current assets	23,400,000	29,500,000
Total current assets	310,400,000	320,400,000
Property, plant and equipment, net	47,300,000	56,200,000
Goodwill	483,400,000	483,400,000
Intangible assets, net	26,900,000	36,500,000
Investment in subsidiaries	0	0
Other assets	7,900,000	6,800,000
Total assets	875,900,000	903,300,000
Current liabilities:
Accounts payable	47,200,000	48,300,000
Accrued expenses	56,800,000	37,000,000
Accrued compensation	32,900,000	36,800,000
Billings in excess of costs and earnings on uncompleted contracts	42,500,000	42,300,000
Amounts due to affiliated companies	0	0
Other current liabilities	6,200,000	6,100,000
Current liabilities of discontinued operations	1,800,000	1,900,000
Total current liabilities	187,400,000	172,400,000
Long-term debt, net of current portion	445,000,000	444,100,000
Other long-term liabilities	35,700,000	28,500,000
Non-current liabilities of discontinued operations	3,700,000	4,100,000
Total liabilities	671,800,000	649,100,000
Total stockholders’ equity	204,100,000	254,200,000
Total liabilities and stockholders’ equity	875,900,000	903,300,000
Eliminations
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Amounts due from affiliated companies	(208,600,000)	(207,800,000)
Inventoried costs	0	0
Other current assets	0	0
Total current assets	(208,600,000)	(207,800,000)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	(517,700,000)	(538,100,000)
Other assets	0	0
Total assets	(726,300,000)	(745,900,000)
Current liabilities:
Accounts payable	0	0
Accrued expenses	0	0
Accrued compensation	0	0
Billings in excess of costs and earnings on uncompleted contracts	0	0
Amounts due to affiliated companies	(208,600,000)	(207,800,000)
Other current liabilities	0	0
Current liabilities of discontinued operations	0	0
Total current liabilities	(208,600,000)	(207,800,000)
Long-term debt, net of current portion	0	0
Other long-term liabilities	0	0
Non-current liabilities of discontinued operations	0	0
Total liabilities	(208,600,000)	(207,800,000)
Total stockholders’ equity	(517,700,000)	(538,100,000)
Total liabilities and stockholders’ equity	$ (726,300,000)	(745,900,000)
Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Ownership percentage (percent)	100.00%
Parent Company
Current assets:
Cash and cash equivalents	$ 15,700,000	22,500,000
Accounts receivable, net	0	0
Amounts due from affiliated companies	208,600,000	207,800,000
Inventoried costs	0	0
Other current assets	6,400,000	16,400,000
Total current assets	230,700,000	246,700,000
Property, plant and equipment, net	1,800,000	2,000,000
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	451,900,000	477,800,000
Other assets	600,000	700,000
Total assets	685,000,000	727,200,000
Current liabilities:
Accounts payable	3,200,000	4,300,000
Accrued expenses	13,400,000	4,700,000
Accrued compensation	3,900,000	4,100,000
Billings in excess of costs and earnings on uncompleted contracts	0	0
Amounts due to affiliated companies	0	0
Other current liabilities	600,000	4,300,000
Current liabilities of discontinued operations	1,700,000	1,800,000
Total current liabilities	22,800,000	19,200,000
Long-term debt, net of current portion	444,000,000	442,400,000
Other long-term liabilities	10,400,000	7,300,000
Non-current liabilities of discontinued operations	3,700,000	4,100,000
Total liabilities	480,900,000	473,000,000
Total stockholders’ equity	204,100,000	254,200,000
Total liabilities and stockholders’ equity	685,000,000	727,200,000
Subsidiary Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	(1,500,000)	(4,800,000)
Accounts receivable, net	177,000,000	179,000,000
Amounts due from affiliated companies	0	0
Inventoried costs	38,000,000	36,900,000
Other current assets	14,800,000	11,700,000
Total current assets	228,300,000	222,800,000
Property, plant and equipment, net	38,700,000	47,500,000
Goodwill	442,600,000	442,600,000
Intangible assets, net	26,900,000	36,500,000
Investment in subsidiaries	65,800,000	60,300,000
Other assets	7,300,000	6,100,000
Total assets	809,600,000	815,800,000
Current liabilities:
Accounts payable	37,300,000	36,500,000
Accrued expenses	40,200,000	29,300,000
Accrued compensation	25,300,000	29,200,000
Billings in excess of costs and earnings on uncompleted contracts	39,500,000	37,100,000
Amounts due to affiliated companies	179,200,000	175,700,000
Other current liabilities	4,000,000	200,000
Current liabilities of discontinued operations	0	0
Total current liabilities	325,500,000	308,000,000
Long-term debt, net of current portion	0	0
Other long-term liabilities	20,200,000	18,000,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	345,700,000	326,000,000
Total stockholders’ equity	463,900,000	489,800,000
Total liabilities and stockholders’ equity	809,600,000	815,800,000
Non-Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	6,300,000	10,800,000
Accounts receivable, net	31,000,000	27,800,000
Amounts due from affiliated companies	0	0
Inventoried costs	20,500,000	18,700,000
Other current assets	2,200,000	1,400,000
Total current assets	60,000,000	58,700,000
Property, plant and equipment, net	6,800,000	6,700,000
Goodwill	40,800,000	40,800,000
Intangible assets, net	0	0
Investment in subsidiaries	0	0
Other assets	0	0
Total assets	107,600,000	106,200,000
Current liabilities:
Accounts payable	6,700,000	7,500,000
Accrued expenses	3,200,000	3,000,000
Accrued compensation	3,700,000	3,500,000
Billings in excess of costs and earnings on uncompleted contracts	3,000,000	5,200,000
Amounts due to affiliated companies	29,400,000	32,100,000
Other current liabilities	1,600,000	1,600,000
Current liabilities of discontinued operations	100,000	100,000
Total current liabilities	47,700,000	53,000,000
Long-term debt, net of current portion	1,000,000	1,700,000
Other long-term liabilities	5,100,000	3,200,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	53,800,000	57,900,000
Total stockholders’ equity	53,800,000	48,300,000
Total liabilities and stockholders’ equity	107,600,000	$ 106,200,000
Senior notes | 7% Senior Notes due 2019
Condensed Financial Statements, Captions [Line Items]
Principal	$ 450,000,000				$ 625,000,000.0