Note 10 - Investments in Affiliates - Summarized Statement of Operations for Equity Method Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue	$ 3,562,459	$ 3,445,606	$ 3,287,031
Gross profit	344,788	221,678	334,840
Income before taxes	(166,463)	(77,078)	8,328
Net income	(166,181)	(56,702)	11,536
Granite’s interest in affiliates’ net income	8,783	11,454	6,935
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Revenue	194,717	261,425	187,827
Gross profit	48,948	57,393	51,061
Income before taxes	28,471	35,391	37,454
Net income	24,073	30,584	31,612
Granite’s interest in affiliates’ net income	$ 8,783	$ 11,454	$ 6,935