Condensed Consolidating Balance Sheet (Details) - USD ($)	Oct. 01, 2017	Dec. 25, 2016	Sep. 25, 2016	Dec. 27, 2015	May 31, 2014
Condensed Financial Statements, Captions [Line Items]
Principal	$ 373,800,000	$ 437,300,000
Current assets:
Cash and cash equivalents	239,200,000	69,100,000	$ 20,500,000	$ 28,500,000
Accounts receivable, net	244,200,000	229,400,000
Amounts due from affiliated companies	0	0
Inventoried costs	62,800,000	55,400,000
Other current assets	21,600,000	19,200,000
Total current assets	567,800,000	373,100,000
Property, plant and equipment, net	56,700,000	49,800,000
Goodwill	485,300,000	485,400,000
Intangible assets, net	24,500,000	32,600,000
Investment in subsidiaries	0	0
Other assets	8,400,000	7,700,000
Total assets	1,142,700,000	948,600,000
Current liabilities:
Accounts payable	50,600,000	52,700,000
Accrued expenses	51,800,000	53,600,000
Accrued compensation	33,700,000	39,100,000
Billings in excess of costs and earnings on uncompleted contracts	51,100,000	41,800,000
Amounts due to affiliated companies	0	0
Other current liabilities	10,500,000	7,700,000
Current liabilities of discontinued operations	1,100,000	1,600,000
Total current liabilities	198,800,000	196,500,000
Long-term debt, net of current portion	369,700,000	431,000,000
Other long-term liabilities	38,500,000	41,000,000
Non-current liabilities of discontinued operations	3,800,000	3,700,000
Total liabilities	610,800,000	672,200,000
Total stockholders’ equity	531,900,000	276,400,000
Total liabilities and stockholders’ equity	1,142,700,000	948,600,000
Eliminations
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Amounts due from affiliated companies	(227,600,000)	(204,600,000)
Inventoried costs	0	0
Other current assets	0	0
Total current assets	(227,600,000)	(204,600,000)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	(537,100,000)	(525,500,000)
Other assets	0	0
Total assets	(764,700,000)	(730,100,000)
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	(227,600,000)	(204,600,000)
Other current liabilities	0	0
Current liabilities of discontinued operations	0	0
Total current liabilities	(227,600,000)	(204,600,000)
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	(227,600,000)	(204,600,000)
Total stockholders’ equity	(537,100,000)	(525,500,000)
Total liabilities and stockholders’ equity	$ (764,700,000)	(730,100,000)
Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Ownership percentage (percent)	100.00%
Parent Company
Current assets:
Cash and cash equivalents	$ 233,000,000	67,200,000
Accounts receivable, net	0	0
Amounts due from affiliated companies	227,600,000	204,600,000
Inventoried costs	0	0
Other current assets	3,600,000	6,300,000
Total current assets	464,200,000	278,100,000
Property, plant and equipment, net	1,900,000	1,600,000
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	469,200,000	458,000,000
Other assets	400,000	400,000
Total assets	935,700,000	738,100,000
Current liabilities:
Accounts payable	1,900,000	4,500,000
Accrued expenses	12,300,000	5,600,000
Accrued compensation	3,500,000	4,000,000
Billings in excess of costs and earnings on uncompleted contracts	0	0
Amounts due to affiliated companies	0	0
Other current liabilities	600,000	1,400,000
Current liabilities of discontinued operations	1,000,000	1,500,000
Total current liabilities	19,300,000	17,000,000
Long-term debt, net of current portion	369,700,000	430,200,000
Other long-term liabilities	11,000,000	10,800,000
Non-current liabilities of discontinued operations	3,800,000	3,700,000
Total liabilities	403,800,000	461,700,000
Total stockholders’ equity	531,900,000	276,400,000
Total liabilities and stockholders’ equity	935,700,000	738,100,000
Subsidiary Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	(2,200,000)	(3,300,000)
Accounts receivable, net	220,400,000	197,900,000
Amounts due from affiliated companies	0	0
Inventoried costs	42,600,000	37,200,000
Other current assets	14,300,000	11,600,000
Total current assets	275,100,000	243,400,000
Property, plant and equipment, net	47,900,000	41,700,000
Goodwill	442,600,000	442,500,000
Intangible assets, net	17,900,000	24,500,000
Investment in subsidiaries	67,900,000	67,500,000
Other assets	8,000,000	7,300,000
Total assets	859,400,000	826,900,000
Current liabilities:
Accounts payable	43,000,000	43,700,000
Accrued expenses	36,900,000	44,500,000
Accrued compensation	27,100,000	31,200,000
Billings in excess of costs and earnings on uncompleted contracts	47,500,000	38,900,000
Amounts due to affiliated companies	198,500,000	174,600,000
Other current liabilities	5,200,000	4,100,000
Current liabilities of discontinued operations	0	0
Total current liabilities	358,200,000	337,000,000
Long-term debt, net of current portion	0	0
Other long-term liabilities	20,000,000	19,900,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	378,200,000	356,900,000
Total stockholders’ equity	481,200,000	470,000,000
Total liabilities and stockholders’ equity	859,400,000	826,900,000
Non-Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	8,400,000	5,200,000
Accounts receivable, net	23,800,000	31,500,000
Amounts due from affiliated companies	0	0
Inventoried costs	20,200,000	18,200,000
Other current assets	3,700,000	1,300,000
Total current assets	56,100,000	56,200,000
Property, plant and equipment, net	6,900,000	6,500,000
Goodwill	42,700,000	42,900,000
Intangible assets, net	6,600,000	8,100,000
Investment in subsidiaries	0	0
Other assets	0	0
Total assets	112,300,000	113,700,000
Current liabilities:
Accounts payable	5,700,000	4,500,000
Accrued expenses	2,600,000	3,500,000
Accrued compensation	3,100,000	3,900,000
Billings in excess of costs and earnings on uncompleted contracts	3,600,000	2,900,000
Amounts due to affiliated companies	29,100,000	30,000,000
Other current liabilities	4,700,000	2,200,000
Current liabilities of discontinued operations	100,000	100,000
Total current liabilities	48,900,000	47,100,000
Long-term debt, net of current portion	0	800,000
Other long-term liabilities	7,500,000	10,300,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	56,400,000	58,200,000
Total stockholders’ equity	55,900,000	55,500,000
Total liabilities and stockholders’ equity	112,300,000	$ 113,700,000
Senior notes | 7% Senior Notes due 2019
Condensed Financial Statements, Captions [Line Items]
Principal	$ 372,800,000.0				$ 625,000,000.0