TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (3,722)	$ (4,201)	$ (3,865)	$ (3,587)	$ (4,063)	$ (4,065)	$ (2,609)	$ (2,135)	$ (15,375)	$ (12,872)	$ (6,798)
Income before income taxes	31,716	32,781	30,504	31,821	30,545	22,646	20,811	19,350	126,822	93,352	77,512
Equity in net income of Tri Counties Bank:
Income tax benefit	(8,826)	(9,386)	(7,443)	(9,095)	(7,334)	(6,476)	(5,782)	(5,440)	(34,750)	(25,032)	(36,958)
Net income	$ 22,890	$ 23,395	$ 23,061	$ 22,726	$ 23,211	$ 16,170	$ 15,029	$ 13,910	92,072	68,320	40,554
Parent
Condensed Financial Statements, Captions [Line Items]
Interest expense									(3,272)	(3,131)	(2,535)
Administration expense									(877)	(1,489)	(915)
Income before income taxes									(4,149)	(4,620)	(3,450)
Equity in net income of Tri Counties Bank:
Distributed									32,669	26,432	19,236
Undistributed									62,326	45,315	23,359
Income tax benefit									1,226	1,193	1,409
Net income									$ 92,072	$ 68,320	$ 40,554