TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (2,135)	$ (1,868)	$ (1,829)	$ (1,610)	$ (1,491)
Income before income taxes	19,350	17,818	19,027	21,236	19,431
Equity in net income of Tri Counties Bank:
Income tax benefit	(5,440)	(14,829)	(7,130)	(7,647)	(7,352)
Net income	13,910	$ 2,989	$ 11,897	$ 13,589	12,079
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Interest expense	(697)				(595)
Administration expense	(426)				(159)
Income before income taxes	(1,123)				(754)
Equity in net income of Tri Counties Bank:
Distributed	4,372				4,042
Undistributed	10,397				8,474
Income tax benefit	264				317
Net income	$ 13,910				$ 12,079