Condensed Consolidating Financial Statements - Balance Sheet (Details) - USD ($)	Mar. 26, 2017	Dec. 25, 2016	Mar. 27, 2016	Dec. 27, 2015	May 31, 2014
Condensed Financial Statements, Captions [Line Items]
Principal	$ 374,300,000	$ 437,300,000
Current assets:
Cash and cash equivalents	73,400,000	69,100,000	$ 20,100,000	$ 28,500,000
Accounts receivable, net	227,900,000	229,400,000
Amounts due from affiliated companies	0	0
Inventoried costs	64,800,000	55,400,000
Other current assets	21,200,000	19,200,000
Total current assets	387,300,000	373,100,000
Property, plant and equipment, net	50,800,000	49,800,000
Goodwill	485,400,000	485,400,000
Intangible assets, net	29,900,000	32,600,000
Investment in subsidiaries	0	0
Other assets	8,200,000	7,700,000
Total assets	961,600,000	948,600,000
Current liabilities:
Accounts payable	51,800,000	52,700,000
Accrued expenses	59,400,000	53,600,000
Accrued compensation	35,200,000	39,100,000
Billings in excess of costs and earnings on uncompleted contracts	41,800,000	41,800,000
Amounts due to affiliated companies	0	0
Other current liabilities	6,400,000	7,700,000
Current liabilities of discontinued operations	1,400,000	1,600,000
Total current liabilities	196,000,000	196,500,000
Long-term debt, net of current portion	369,300,000	431,000,000
Other long-term liabilities	41,200,000	41,000,000
Non-current liabilities of discontinued operations	3,700,000	3,700,000
Total liabilities	610,200,000	672,200,000
Total stockholders’ equity	351,400,000	276,400,000
Total liabilities and stockholders’ equity	961,600,000	948,600,000
Eliminations
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Amounts due from affiliated companies	(219,800,000)	(204,600,000)
Inventoried costs	0	0
Other current assets	0	0
Total current assets	(219,800,000)	(204,600,000)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	(527,800,000)	(525,500,000)
Other assets	0	0
Total assets	(747,600,000)	(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	(219,800,000)	(204,600,000)
Other current liabilities	0	0
Current liabilities of discontinued operations	0	0
Total current liabilities	(219,800,000)	(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	(219,800,000)	(204,600,000)
Total stockholders’ equity	(527,800,000)	(525,500,000)
Total liabilities and stockholders’ equity	$ (747,600,000)	(730,100,000)
Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Ownership percentage	100.00%
Parent Company
Current assets:
Cash and cash equivalents	$ 68,900,000	67,200,000
Accounts receivable, net	0	0
Amounts due from affiliated companies	219,800,000	204,600,000
Inventoried costs	0	0
Other current assets	4,700,000	6,300,000
Total current assets	293,400,000	278,100,000
Property, plant and equipment, net	1,500,000	1,600,000
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	460,600,000	458,000,000
Other assets	300,000	400,000
Total assets	755,800,000	738,100,000
Current liabilities:
Accounts payable	3,600,000	4,500,000
Accrued expenses	11,300,000	5,600,000
Accrued compensation	4,000,000	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	900,000	1,400,000
Current liabilities of discontinued operations	1,300,000	1,500,000
Total current liabilities	21,100,000	17,000,000
Long-term debt, net of current portion	368,800,000	430,200,000
Other long-term liabilities	10,800,000	10,800,000
Non-current liabilities of discontinued operations	3,700,000	3,700,000
Total liabilities	404,400,000	461,700,000
Total stockholders’ equity	351,400,000	276,400,000
Total liabilities and stockholders’ equity	755,800,000	738,100,000
Subsidiary Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	(1,100,000)	(3,300,000)
Accounts receivable, net	198,100,000	197,900,000
Amounts due from affiliated companies	0	0
Inventoried costs	45,900,000	37,200,000
Other current assets	13,800,000	11,600,000
Total current assets	256,700,000	243,400,000
Property, plant and equipment, net	42,800,000	41,700,000
Goodwill	442,500,000	442,500,000
Intangible assets, net	22,300,000	24,500,000
Investment in subsidiaries	67,200,000	67,500,000
Other assets	7,900,000	7,300,000
Total assets	839,400,000	826,900,000
Current liabilities:
Accounts payable	43,100,000	43,700,000
Accrued expenses	44,300,000	44,500,000
Accrued compensation	26,800,000	31,200,000
Billings in excess of costs and earnings on uncompleted contracts	36,900,000	38,900,000
Amounts due to affiliated companies	192,000,000	174,600,000
Other current liabilities	3,800,000	4,100,000
Current liabilities of discontinued operations	0	0
Total current liabilities	346,900,000	337,000,000
Long-term debt, net of current portion	0	0
Other long-term liabilities	19,900,000	19,900,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	366,800,000	356,900,000
Total stockholders’ equity	472,600,000	470,000,000
Total liabilities and stockholders’ equity	839,400,000	826,900,000
Non-Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	5,600,000	5,200,000
Accounts receivable, net	29,800,000	31,500,000
Amounts due from affiliated companies	0	0
Inventoried costs	18,900,000	18,200,000
Other current assets	2,700,000	1,300,000
Total current assets	57,000,000	56,200,000
Property, plant and equipment, net	6,500,000	6,500,000
Goodwill	42,900,000	42,900,000
Intangible assets, net	7,600,000	8,100,000
Investment in subsidiaries	0	0
Other assets	0	0
Total assets	114,000,000	113,700,000
Current liabilities:
Accounts payable	5,100,000	4,500,000
Accrued expenses	3,800,000	3,500,000
Accrued compensation	4,400,000	3,900,000
Billings in excess of costs and earnings on uncompleted contracts	4,900,000	2,900,000
Amounts due to affiliated companies	27,800,000	30,000,000
Other current liabilities	1,700,000	2,200,000
Current liabilities of discontinued operations	100,000	100,000
Total current liabilities	47,800,000	47,100,000
Long-term debt, net of current portion	500,000	800,000
Other long-term liabilities	10,500,000	10,300,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	58,800,000	58,200,000
Total stockholders’ equity	55,200,000	55,500,000
Total liabilities and stockholders’ equity	114,000,000	$ 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