Condensed Consolidating Balance Sheet (Details) - USD ($)	Jun. 25, 2017	Dec. 25, 2016	Jun. 26, 2016	Dec. 27, 2015	May 31, 2014
Condensed Financial Statements, Captions [Line Items]
Principal	$ 374,100,000	$ 437,300,000
Current assets:
Cash and cash equivalents	63,300,000	69,100,000	$ 17,600,000	$ 28,500,000
Accounts receivable, net	226,600,000	229,400,000
Amounts due from affiliated companies	0	0
Inventoried costs	61,500,000	55,400,000
Other current assets	22,400,000	19,200,000
Total current assets	373,800,000	373,100,000
Property, plant and equipment, net	55,000,000	49,800,000
Goodwill	485,400,000	485,400,000
Intangible assets, net	27,300,000	32,600,000
Investment in subsidiaries	0	0
Other assets	8,500,000	7,700,000
Total assets	950,000,000	948,600,000
Current liabilities:
Accounts payable	55,800,000	52,700,000
Accrued expenses	48,100,000	53,600,000
Accrued compensation	35,600,000	39,100,000
Billings in excess of costs and earnings on uncompleted contracts	40,300,000	41,800,000
Amounts due to affiliated companies	0	0
Other current liabilities	6,100,000	7,700,000
Current liabilities of discontinued operations	1,200,000	1,600,000
Total current liabilities	187,100,000	196,500,000
Long-term debt, net of current portion	369,500,000	431,000,000
Other long-term liabilities	42,600,000	41,000,000
Non-current liabilities of discontinued operations	3,800,000	3,700,000
Total liabilities	603,000,000	672,200,000
Total stockholders’ equity	347,000,000	276,400,000
Total liabilities and stockholders’ equity	950,000,000	948,600,000
Eliminations
Current assets:
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Amounts due from affiliated companies	(215,800,000)	(204,600,000)
Inventoried costs	0	0
Other current assets	0	0
Total current assets	(215,800,000)	(204,600,000)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	(529,800,000)	(525,500,000)
Other assets	0	0
Total assets	(745,600,000)	(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	(215,800,000)	(204,600,000)
Other current liabilities	0	0
Current liabilities of discontinued operations	0	0
Total current liabilities	(215,800,000)	(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	(215,800,000)	(204,600,000)
Total stockholders’ equity	(529,800,000)	(525,500,000)
Total liabilities and stockholders’ equity	$ (745,600,000)	(730,100,000)
Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Ownership percentage (percent)	100.00%
Parent Company
Current assets:
Cash and cash equivalents	$ 59,600,000	67,200,000
Accounts receivable, net	0	0
Amounts due from affiliated companies	215,800,000	204,600,000
Inventoried costs	0	0
Other current assets	3,600,000	6,300,000
Total current assets	279,000,000	278,100,000
Property, plant and equipment, net	1,400,000	1,600,000
Goodwill	0	0
Intangible assets, net	0	0
Investment in subsidiaries	463,100,000	458,000,000
Other assets	400,000	400,000
Total assets	743,900,000	738,100,000
Current liabilities:
Accounts payable	3,100,000	4,500,000
Accrued expenses	4,400,000	5,600,000
Accrued compensation	4,200,000	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	400,000	1,400,000
Current liabilities of discontinued operations	1,100,000	1,500,000
Total current liabilities	13,200,000	17,000,000
Long-term debt, net of current portion	369,200,000	430,200,000
Other long-term liabilities	10,700,000	10,800,000
Non-current liabilities of discontinued operations	3,800,000	3,700,000
Total liabilities	396,900,000	461,700,000
Total stockholders’ equity	347,000,000	276,400,000
Total liabilities and stockholders’ equity	743,900,000	738,100,000
Subsidiary Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	(1,700,000)	(3,300,000)
Accounts receivable, net	197,000,000	197,900,000
Amounts due from affiliated companies	0	0
Inventoried costs	43,100,000	37,200,000
Other current assets	14,200,000	11,600,000
Total current assets	252,600,000	243,400,000
Property, plant and equipment, net	47,400,000	41,700,000
Goodwill	442,600,000	442,500,000
Intangible assets, net	20,100,000	24,500,000
Investment in subsidiaries	66,700,000	67,500,000
Other assets	8,100,000	7,300,000
Total assets	837,500,000	826,900,000
Current liabilities:
Accounts payable	45,500,000	43,700,000
Accrued expenses	41,000,000	44,500,000
Accrued compensation	27,100,000	31,200,000
Billings in excess of costs and earnings on uncompleted contracts	36,000,000	38,900,000
Amounts due to affiliated companies	187,200,000	174,600,000
Other current liabilities	4,100,000	4,100,000
Current liabilities of discontinued operations	0	0
Total current liabilities	340,900,000	337,000,000
Long-term debt, net of current portion	0	0
Other long-term liabilities	21,500,000	19,900,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	362,400,000	356,900,000
Total stockholders’ equity	475,100,000	470,000,000
Total liabilities and stockholders’ equity	837,500,000	826,900,000
Non-Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	5,400,000	5,200,000
Accounts receivable, net	29,600,000	31,500,000
Amounts due from affiliated companies	0	0
Inventoried costs	18,400,000	18,200,000
Other current assets	4,600,000	1,300,000
Total current assets	58,000,000	56,200,000
Property, plant and equipment, net	6,200,000	6,500,000
Goodwill	42,800,000	42,900,000
Intangible assets, net	7,200,000	8,100,000
Investment in subsidiaries	0	0
Other assets	0	0
Total assets	114,200,000	113,700,000
Current liabilities:
Accounts payable	7,200,000	4,500,000
Accrued expenses	2,700,000	3,500,000
Accrued compensation	4,300,000	3,900,000
Billings in excess of costs and earnings on uncompleted contracts	4,300,000	2,900,000
Amounts due to affiliated companies	28,600,000	30,000,000
Other current liabilities	1,600,000	2,200,000
Current liabilities of discontinued operations	100,000	100,000
Total current liabilities	48,800,000	47,100,000
Long-term debt, net of current portion	300,000	800,000
Other long-term liabilities	10,400,000	10,300,000
Non-current liabilities of discontinued operations	0	0
Total liabilities	59,500,000	58,200,000
Total stockholders’ equity	54,700,000	55,500,000
Total liabilities and stockholders’ equity	114,200,000	$ 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