TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (2,609)	$ (2,135)	$ (1,868)	$ (1,829)	$ (1,610)	$ (1,491)	$ (4,744)	$ (3,101)
Income before income taxes	20,811	19,350	17,818	19,027	21,236	19,431	40,161	40,667
Equity in net income of Tri Counties Bank:
Income tax benefit	(5,782)	(5,440)	(14,829)	(7,130)	(7,647)	(7,352)	(11,222)	(14,999)
Net income	15,029	$ 13,910	$ 2,989	$ 11,897	13,589	$ 12,079	28,939	25,668
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Interest expense	(789)				(623)		(1,486)	(1,218)
Administration expense	(511)				(218)		(937)	(377)
Income before income taxes	(1,300)				(841)		(2,423)	(1,595)
Equity in net income of Tri Counties Bank:
Distributed	4,770				5,167		9,142	9,209
Undistributed	11,253				8,909		21,650	17,383
Income tax benefit	306				354		570	671
Net income	$ 15,029				$ 13,589		$ 28,939	$ 25,668