TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 182,979	$ 205,428	$ 323,706	$ 305,612
Other assets	56,274	55,051
Total assets	4,779,957	4,761,315
Liabilities and shareholders' equity
Other liabilities	63,529	63,258
Junior subordinated debt	56,905	56,858
Total liabilities	4,274,701	4,255,507
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 22,956,323 and 22,955,963 shares, respectively	256,226	255,836
Retained earnings	266,235	255,200
Accumulated other comprehensive loss, net	(17,205)	(5,228)	(7,402)
Total shareholders' equity	505,256	505,808	486,718	477,347
Total liabilities and shareholders' equity	4,779,957	4,761,315
Parent [Member]
Assets
Cash and cash equivalents	3,516	3,924	$ 2,840	$ 2,802
Investment in Tri Counties Bank	557,380	557,538
Other assets	1,758	1,721
Total assets	562,654	563,183
Liabilities and shareholders' equity
Other liabilities	493	517
Junior subordinated debt	56,905	56,858
Total liabilities	57,398	57,375
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 22,956,323 and 22,955,963 shares, respectively	256,226	255,836
Retained earnings	266,235	255,200
Accumulated other comprehensive loss, net	(17,205)	(5,228)
Total shareholders' equity	505,256	505,808
Total liabilities and shareholders' equity	$ 562,654	$ 563,183