TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (1,659)	$ (1,984)	$ (2,489)	$ (3,325)	$ (3,722)	$ (4,201)	$ (3,865)	$ (3,587)	$ (9,457)	$ (15,375)	$ (12,872)
Income before income taxes	32,407	24,228	8,522	22,193	31,716	32,781	30,504	31,821	87,350	126,822	93,352
Equity in net income of Tri Counties Bank:
Income tax benefit	(8,750)	(6,622)	(1,092)	(6,072)	(8,826)	(9,386)	(7,443)	(9,095)	(22,536)	(34,750)	(25,032)
Net income	$ 23,657	$ 17,606	$ 7,430	$ 16,121	$ 22,890	$ 23,395	$ 23,061	$ 22,726	64,814	92,072	68,320
Parent
Condensed Financial Statements, Captions [Line Items]
Interest expense									(2,555)	(3,272)	(3,131)
Administration expense									(932)	(877)	(1,489)
Income before income taxes									(3,487)	(4,149)	(4,620)
Equity in net income of Tri Counties Bank:
Distributed									63,419	32,669	26,432
Undistributed									3,851	62,326	45,315
Income tax benefit									1,031	1,226	1,193
Net income									$ 64,814	$ 92,072	$ 68,320