Summary of Significant Accounting Policies - Recent Accounting Standards Not Yet Adopted (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Dec. 29, 2019	Dec. 28, 2019	Dec. 30, 2018	Dec. 29, 2018
Recent Accounting Standards
CRA elected package of practical expedients	true
Operating lease right-of-use assets	$ 125,688		$ 130,173
Cumulative-effect adjustment to allowances for accounts receivable	494		370		$ 639
Cumulative-effect adjustment to retained earnings	204,679		200,249
Cumulative-effect adjustment to unbilled services	$ 44,377		$ 36,569
ASU 2016-02
Recent Accounting Standards
Operating lease right-of-use assets				$ 82,300
Recognize lease liabilities				$ 106,800
ASU 2016-13 Financial Instruments-Credit Losses Topic 326 | Restatement adjustment
Recent Accounting Standards
Cumulative-effect adjustment to allowances for accounts receivable		$ 200
Cumulative-effect adjustment to retained earnings		200
Cumulative-effect adjustment to unbilled services		$ 200