Consolidated Variable Interest Entities - Statements of Operations (Details) - USD ($) $ in Thousands	3 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	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	$ 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	2,098,153	2,183,574	1,991,622
Selling, general and administrative expenses									498,827	530,080	536,019
Total operating expenses									2,631,134	2,746,859	2,563,421
Program profit									83,494	17,034	45,141
Other income (loss), net									7,272	9,785	4,980
Net income (loss)									15,290	(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)