TriCo Bancshares Condensed Financial Statements (Parent Only) - Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ (1,868)	$ (1,829)	$ (1,610)	$ (1,491)	$ (1,460)	$ (1,439)	$ (1,430)	$ (1,392)	$ (6,798)	$ (5,721)	$ (5,416)
Income before income taxes	17,818	19,027	21,236	19,431	20,487	19,893	14,911	17,232	77,512	72,523	72,714
Equity in net income of Tri Counties Bank:
Income tax benefit	(14,829)	(7,130)	(7,647)	(7,352)	(7,954)	(7,694)	(5,506)	(6,558)	(36,958)	(27,712)	(28,896)
Net income	$ 2,989	$ 11,897	$ 13,589	$ 12,079	$ 12,533	$ 12,199	$ 9,405	$ 10,674	40,554	44,811	43,818
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Interest expense									(2,535)	(2,229)	(1,977)
Administration expense									(915)	(725)	(814)
Income before income taxes									(3,450)	(2,954)	(2,791)
Equity in net income of Tri Counties Bank:
Distributed									19,236	16,758	13,304
Undistributed									23,359	29,764	32,131
Income tax benefit									1,409	1,243	1,174
Net income									$ 40,554	$ 44,811	$ 43,818