TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 184,062	$ 205,428
Other assets	57,409	55,051
Total assets	4,863,153	4,761,315
Liabilities and shareholders' equity
Other liabilities	58,896	63,258
Junior subordinated debt	56,950	56,858
Total liabilities	4,350,809	4,255,507
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at June 30, 2018 and December 31, 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 23,004,153 and 22,955,963 shares, respectively	256,590	255,836
Retained earnings	276,877	255,200
Accumulated other comprehensive loss, net	(21,123)	(5,228)
Total shareholders' equity	512,344	505,808	$ 498,944	$ 477,347
Total liabilities and shareholders' equity	4,863,153	4,761,315
Parent [Member]
Assets
Cash and cash equivalents	3,069	3,924
Investment in Tri Counties Bank	565,047	557,538
Other assets	1,742	1,721
Total assets	569,858	563,183
Liabilities and shareholders' equity
Other liabilities	564	517
Junior subordinated debt	56,950	56,858
Total liabilities	57,514	57,375
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at June 30, 2018 and December 31, 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 23,004,153 and 22,955,963 shares, respectively	256,590	255,836
Retained earnings	276,877	255,200
Accumulated other comprehensive loss, net	(21,123)	(5,228)
Total shareholders' equity	512,344	505,808
Total liabilities and shareholders' equity	$ 569,858	$ 563,183