TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (4,063)	$ (4,065)	$ (2,609)	$ (2,135)	$ (1,868)	$ (1,829)	$ (1,610)	$ (1,491)	$ (12,872)	$ (6,798)	$ (5,721)
Income before income taxes	30,545	22,646	20,811	19,350	17,818	19,027	21,236	19,431	93,352	77,512	72,523
Equity in net income of Tri Counties Bank:
Income tax benefit	(7,334)	(6,476)	(5,782)	(5,440)	(14,829)	(7,130)	(7,647)	(7,352)	(25,032)	(36,958)	(27,712)
Net income	$ 23,211	$ 16,170	$ 15,029	$ 13,910	$ 2,989	$ 11,897	$ 13,589	$ 12,079	68,320	40,554	44,811
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Interest expense									(3,131)	(2,535)	(2,229)
Administration expense									(1,489)	(915)	(725)
Income before income taxes									(4,620)	(3,450)	(2,954)
Equity in net income of Tri Counties Bank:
Distributed									26,432	19,236	16,758
Undistributed									45,315	23,359	29,764
Income tax benefit									1,193	1,409	1,243
Net income									$ 68,320	$ 40,554	$ 44,811