Consolidated Variable Interest Entities - Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Variable Interest Entity [Line Items]
Revenues	$ 643,303	$ 695,607	$ 1,260,556	$ 1,369,091
Cost of revenues	496,678	540,772	961,886	1,057,931
Selling, general and administrative expenses	105,451	126,438	242,777	261,474
Total operating expenses	610,176	675,406	1,220,757	1,336,258
Program profit	33,127	20,201	39,799	32,833
Other (income) expense, net	1,168	5,958	1,954	7,678
Net income (loss)	16,021	2,674	11,078	(3,046)
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Revenues	94,454	89,789	181,644	153,049
Cost of revenues	76,634	71,552	145,159	121,954
Selling, general and administrative expenses	15,864	21,438	33,881	39,727
Total operating expenses	92,498	92,990	179,040	161,681
Program profit	1,956	(3,201)	2,604	(8,632)
Other (income) expense, net	840	(500)	(209)	(854)
Net income (loss)	$ 2,796	$ (3,701)	$ 2,395	$ (9,486)