Acquisitions (Details)				3 Months Ended		6 Months Ended
	Jan. 01, 2017 USD ($)	Jun. 18, 2016 USD ($)	Jan. 05, 2016 USD ($) customer	Jun. 30, 2017 USD ($)	Jul. 01, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jul. 01, 2016 USD ($)	Dec. 30, 2016 USD ($)
Acquisitions
Revenues				$ 200,733,000	$ 155,996,000	$ 402,045,000	$ 309,694,000
Operating income				9,831,000	9,498,000	16,895,000	17,234,000
Approximate fair value estimates of the assets acquired and liabilities assumed
Goodwill				389,258,000		389,258,000		$ 305,476,000
LTS
Approximate fair value estimates of the assets acquired and liabilities assumed
Interest acquired (as a percent)			100.00%
Concentrations (as a percent)			74.00%
Number of customers | customer			2
Purchase price			$ 37,000,000
Bayonne
Approximate fair value estimates of the assets acquired and liabilities assumed
Purchase price			$ 4,100,000
The Wisconsin acquisition
Approximate fair value estimates of the assets acquired and liabilities assumed
Accounts receivable		$ 0
Purchase price		$ 6,100,000
Community Health Systems Inc.
Acquisitions
Revenues						98,100,000	98,400,000
Operating income						17,900,000	4,500,000
Deal and transition costs incurred						3,900,000
Approximate fair value estimates of the assets acquired and liabilities assumed
Accounts receivable				21,020,000		21,020,000
Prepaids and other assets				705,000		705,000
Property, plant & equipment				8,423,000		8,423,000
Goodwill				83,782,000		83,782,000
Intangibles				61,800,000		61,800,000
Assets acquired				175,730,000		175,730,000
Liabilities assumed				(14,759,000)		(14,759,000)
Non-controlling interest				(32,042,000)		(32,042,000)
Net assets acquired				128,929,000		128,929,000
Interest acquired (as a percent)	80.00%
Purchase price	$ 128,900,000
Healthcare Innovations
Acquisitions
Revenues				5,841,000	$ 5,644,000	10,400,000	$ 10,036,000
Approximate fair value estimates of the assets acquired and liabilities assumed
Goodwill				$ 36,649,000		$ 36,649,000
Interest acquired (as a percent)				72.00%	61.50%	72.00%	61.50%