Consolidated Variable Interest Entities - Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 27, 2020	Jun. 28, 2020	Mar. 29, 2020	Dec. 31, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 28, 2020	Sep. 27, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Revenues	$ 787,833	$ 666,240	$ 643,303	$ 617,253	$ 697,085	$ 697,717	$ 695,607	$ 673,484	$ 1,260,556	$ 1,926,795	$ 2,714,628	$ 2,763,893	$ 2,608,562
Cost of revenues	$ 623,390	512,877	496,678	465,208	$ 559,940	$ 565,703	$ 540,772	$ 517,159	961,886	1,474,763	2,098,153	2,183,574	1,991,622
Selling, general and administrative expenses		119,168	105,451	137,326					242,777	361,945	498,827	530,080	536,019
Total operating expenses		640,092	610,176	610,581					1,220,757	1,860,849	2,631,134	2,746,859	2,563,421
Program profit		26,148	33,127	6,672					39,799	65,946	83,494	17,034	45,141
Other income (loss), net		2,384	1,168	785					1,954	4,338	7,272	9,785	4,980
Net income (loss)		$ 15,318	$ (3,446)	$ 25,984					$ 22,538	$ 37,855	28,750	(49,809)	(34,459)
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Revenues											369,966	340,063	259,386
Cost of revenues											301,345	311,310	205,730
Selling, general and administrative expenses											73,400	80,942	84,473
Total operating expenses											374,745	392,252	290,203
Program profit											(4,779)	(52,189)	(30,817)
Other income (loss), net											908	(1,697)	(1,093)
Net income (loss)											$ (3,871)	$ (53,886)	$ (31,910)