TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Operating activities:
Net income	$ 13,910	$ 2,989	$ 11,897	$ 13,589	$ 12,079
Adjustments to reconcile net income to net cash provided by operating activities:
Equity compensation vesting expense	391				381
Net cash from operating activities	23,714				19,444
Financing activities:
Repurchase of common stock					(169)
Cash dividends paid - common	(3,903)				(3,431)
Net cash used by financing activities	14,245				(2,572)
Net change in cash and cash equivalents	(22,449)				18,094
Cash and cash equivalents and beginning of year	205,428			323,706	305,612
Cash and cash equivalents at end of year	182,979	205,428			323,706
Parent [Member]
Operating activities:
Net income	13,910				12,079
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed equity in earnings of Tri Counties Bank	(10,397)				(8,474)
Equity compensation vesting expense	391				381
Stock option excess tax benefits	0				0
Net change in other assets and liabilities	(405)				(348)
Net cash from operating activities	3,499				3,638
Financing activities:
Repurchase of common stock	(4)				(169)
Cash dividends paid - common	(3,903)				(3,431)
Net cash used by financing activities	(3,907)				(3,600)
Net change in cash and cash equivalents	(408)				38
Cash and cash equivalents and beginning of year	3,924			$ 2,840	2,802
Cash and cash equivalents at end of year	$ 3,516	$ 3,924			$ 2,840