Acquisitions (Details) - USD ($) $ in Thousands		3 Months Ended
	Apr. 01, 2019	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Consideration transferred:
Total consideration transferred		$ 1,600
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 347,391	$ 332,447	$ 235,182
Walker
Consideration transferred:
Cash paid at closing	$ 178,000
Advance to former owners	20,500
Working capital adjustment	(7,809)
Notes issued to former owners	25,000
Tax equalization payment	202
Estimated fair value of contingent earn-out payments	19,500
Total consideration transferred	235,393
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents	4,850
Billed and unbilled accounts receivable	92,309
Other current assets	8,225
Other long-term assets	53
Property and equipment	4,970
Goodwill	96,786
Identifiable intangible assets	90,200
Lease right-of-use asset	9,195
Accounts payable	(20,220)
Accrued compensation and benefits	(974)
Billings in excess of costs and estimated earnings	(31,553)
Other current liabilities	(11,305)
Long-term lease liabilities	(7,143)
Total assets acquired and liabilities assumed	$ 235,393
Cash flow discount rate	10.20%
Walker | Minimum
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash flow discount rate	8.50%
Walker | Maximum
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash flow discount rate	11.50%