TriCo Bancshares Condensed Financial Statements (Parent Only) - Statements of Cash Flows (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
Operating activities:
Net income	$ 2,989	$ 11,897	$ 13,589	$ 12,079	$ 12,533	$ 12,199	$ 9,405	$ 10,674	$ 40,554	$ 44,811	$ 43,818
Adjustments to reconcile net income to net cash provided by operating activities:
Equity compensation vesting expense									1,586	1,467	1,370
Net cash from operating activities									55,381	48,226	54,817
Financing activities:
Equity compensation tax effect										155	(68)
Repurchase of common stock									(1,629)	(1,890)	(412)
Cash dividends paid - common									(15,131)	(13,695)	(11,849)
Net cash from financing activities									201,880	93,316	242,226
Net change in cash and cash equivalents									(100,184)	2,151	(307,267)
Cash and cash equivalents and beginning of year				305,612				303,461	305,612	303,461	610,728
Cash and cash equivalents at end of year	205,428				305,612				205,428	305,612	303,461
Parent [Member]
Operating activities:
Net income									40,554	44,811	43,818
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed equity in earnings of Tri Counties Bank									(23,359)	(29,764)	(32,131)
Equity compensation vesting expense									1,586	1,467	1,370
Equity compensation tax effect										(155)	68
Net change in other assets and liabilities									(1,295)	(1,210)	(1,120)
Net cash from operating activities									17,486	15,149	12,005
Financing activities:
Issuance of common stock through option exercise									396	518	660
Equity compensation tax effect										155	(68)
Repurchase of common stock									(1,629)	(1,890)	(412)
Cash dividends paid - common									(15,131)	(13,695)	(11,849)
Net cash from financing activities									(16,364)	(14,912)	(11,669)
Net change in cash and cash equivalents									1,122	237	336
Cash and cash equivalents and beginning of year				$ 2,802				$ 2,565	2,802	2,565	2,229
Cash and cash equivalents at end of year	$ 3,924				$ 2,802				$ 3,924	$ 2,802	$ 2,565