Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($)	Dec. 31, 2017	Nov. 30, 2017	Dec. 25, 2016	Dec. 27, 2015	Dec. 28, 2014	May 31, 2014
Condensed Financial Statements, Captions [Line Items]
Principal	$ 300,800,000.0		$ 437,300,000.0
Ownership percentage	100.00%
Current assets:
Cash and cash equivalents	$ 129,600,000		69,100,000	$ 28,500,000	$ 33,500,000
Accounts receivable, net	268,400,000		229,400,000
Amounts due from affiliated companies	0		0
Inventoried costs	50,400,000		55,400,000
Other current assets	22,900,000		19,200,000
Total current assets	471,300,000		373,100,000
Property, plant and equipment, net	61,200,000		49,800,000
Goodwill	461,200,000		485,400,000
Intangible assets, net	22,000,000		32,600,000
Investment in subsidiaries	0		0
Other assets	8,300,000		7,700,000
Total assets	1,024,000,000		948,600,000	903,300,000
Current liabilities:
Accounts payable	48,800,000		52,700,000
Accrued expenses	47,300,000		53,600,000
Accrued compensation	34,800,000		39,100,000
Billings in excess of costs and earnings on uncompleted contracts	47,200,000		41,800,000
Amounts due to affiliated companies	0		0
Other current liabilities	9,700,000		7,700,000
Current liabilities of discontinued operations	1,100,000		1,600,000
Total current liabilities	188,900,000		196,500,000
Long-term debt, net of current portion	293,500,000		431,000,000
Other long-term liabilities	26,300,000		41,000,000
Non-current liabilities of discontinued operations	3,800,000		3,700,000
Total liabilities	512,500,000		672,200,000
Total stockholders’ equity	511,500,000		276,400,000	$ 254,200,000	$ 224,300,000
Total liabilities and stockholders’ equity	1,024,000,000		948,600,000
Eliminations
Current assets:
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Amounts due from affiliated companies	(238,100,000)		(204,600,000)
Inventoried costs	0		0
Other current assets	0		0
Total current assets	(238,100,000)		(204,600,000)
Property, plant and equipment, net	0		0
Goodwill	0		0
Intangible assets, net	0		0
Investment in subsidiaries	(541,100,000)		(525,500,000)
Other assets	0		0
Total assets	(779,200,000)		(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	(238,100,000)		(204,600,000)
Other current liabilities	0		0
Current liabilities of discontinued operations	0		0
Total current liabilities	(238,100,000)		(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	(238,100,000)		(204,600,000)
Total stockholders’ equity	(541,100,000)		(525,500,000)
Total liabilities and stockholders’ equity	(779,200,000)		(730,100,000)
Parent Company
Current assets:
Cash and cash equivalents	121,100,000		67,200,000
Accounts receivable, net	0		0
Amounts due from affiliated companies	238,100,000		204,600,000
Inventoried costs	0		0
Other current assets	3,900,000		6,300,000
Total current assets	363,100,000		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	471,100,000		458,000,000
Other assets	800,000		400,000
Total assets	836,900,000		738,100,000
Current liabilities:
Accounts payable	2,300,000		4,500,000
Accrued expenses	5,700,000		5,600,000
Accrued compensation	5,600,000		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	1,400,000		1,400,000
Current liabilities of discontinued operations	1,000,000		1,500,000
Total current liabilities	16,000,000		17,000,000
Long-term debt, net of current portion	293,500,000		430,200,000
Other long-term liabilities	12,100,000		10,800,000
Non-current liabilities of discontinued operations	3,800,000		3,700,000
Total liabilities	325,400,000		461,700,000
Total stockholders’ equity	511,500,000		276,400,000
Total liabilities and stockholders’ equity	836,900,000		738,100,000
Subsidiary Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	(2,200,000)		(3,300,000)
Accounts receivable, net	239,900,000		197,900,000
Amounts due from affiliated companies	0		0
Inventoried costs	32,200,000		37,200,000
Other current assets	15,600,000		11,600,000
Total current assets	285,500,000		243,400,000
Property, plant and equipment, net	52,500,000		41,700,000
Goodwill	418,300,000		442,500,000
Intangible assets, net	15,800,000		24,500,000
Investment in subsidiaries	70,000,000		67,500,000
Other assets	7,500,000		7,300,000
Total assets	849,600,000		826,900,000
Current liabilities:
Accounts payable	42,000,000		43,700,000
Accrued expenses	38,300,000		44,500,000
Accrued compensation	25,300,000		31,200,000
Billings in excess of costs and earnings on uncompleted contracts	42,600,000		38,900,000
Amounts due to affiliated companies	206,400,000		174,600,000
Other current liabilities	4,600,000		4,100,000
Current liabilities of discontinued operations	0		0
Total current liabilities	359,200,000		337,000,000
Long-term debt, net of current portion	0		0
Other long-term liabilities	7,300,000		19,900,000
Non-current liabilities of discontinued operations	0		0
Total liabilities	366,500,000		356,900,000
Total stockholders’ equity	483,100,000		470,000,000
Total liabilities and stockholders’ equity	849,600,000		826,900,000
Non-Guarantors on a Combined Basis
Current assets:
Cash and cash equivalents	10,700,000		5,200,000
Accounts receivable, net	28,500,000		31,500,000
Amounts due from affiliated companies	0		0
Inventoried costs	18,200,000		18,200,000
Other current assets	3,400,000		1,300,000
Total current assets	60,800,000		56,200,000
Property, plant and equipment, net	6,800,000		6,500,000
Goodwill	42,900,000		42,900,000
Intangible assets, net	6,200,000		8,100,000
Investment in subsidiaries	0		0
Other assets	0		0
Total assets	116,700,000		113,700,000
Current liabilities:
Accounts payable	4,500,000		4,500,000
Accrued expenses	3,300,000		3,500,000
Accrued compensation	3,900,000		3,900,000
Billings in excess of costs and earnings on uncompleted contracts	4,600,000		2,900,000
Amounts due to affiliated companies	31,700,000		30,000,000
Other current liabilities	3,700,000		2,200,000
Current liabilities of discontinued operations	100,000		100,000
Total current liabilities	51,800,000		47,100,000
Long-term debt, net of current portion	0		800,000
Other long-term liabilities	6,900,000		10,300,000
Non-current liabilities of discontinued operations	0		0
Total liabilities	58,700,000		58,200,000
Total stockholders’ equity	58,000,000		55,500,000
Total liabilities and stockholders’ equity	116,700,000		$ 113,700,000
Senior notes | 7% Senior Notes due 2019
Condensed Financial Statements, Captions [Line Items]
Principal	$ 300,000,000					$ 625,000,000.0
Stated interest rate	7.00%					7.00%
Senior notes | 6.5% Notes
Condensed Financial Statements, Captions [Line Items]
Principal		$ 300,000,000
Stated interest rate	6.50%	6.50%