TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 669,551	$ 276,507
Other assets	84,172	70,591
Total assets	7,639,529	6,471,181
Liabilities and shareholders’ equity
Other liabilities	94,597	91,984
Junior subordinated debt	57,635	57,232
Total liabilities	6,714,415	5,564,611
Shareholders’ equity:
Preferred stock, value issued	0	0
Common stock, no par value: 50,000,000 shares authorized; issued and outstanding: 29,727,214 and 30,523,824 at December 31, 2020 and 2019, respectively	530,835	543,998
Retained earnings	381,999	367,794
Accumulated other comprehensive loss, net	12,280	(5,222)
Total shareholders’ equity	925,114	906,570	$ 827,373	$ 505,808
Total liabilities and shareholders’ equity	7,639,529	6,471,181
Parent
Assets
Cash and cash equivalents	13,297	5,008
Investment in Tri Counties Bank	967,949	957,544
Other assets	1,818	1,765
Total assets	983,064	964,317
Liabilities and shareholders’ equity
Other liabilities	315	515
Junior subordinated debt	57,635	57,232
Total liabilities	57,950	57,747
Shareholders’ equity:
Preferred stock, value issued	0	0
Common stock, no par value: 50,000,000 shares authorized; issued and outstanding: 29,727,214 and 30,523,824 at December 31, 2020 and 2019, respectively	530,835	543,998
Retained earnings	381,999	367,794
Accumulated other comprehensive loss, net	12,280	(5,222)
Total shareholders’ equity	925,114	906,570
Total liabilities and shareholders’ equity	$ 983,064	$ 964,317