TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 227,533	$ 205,428
Other assets	65,986	55,051
Total assets	6,352,441	4,761,315
Liabilities and shareholders' equity
Other liabilities	83,724	66,422
Junior subordinated debt	57,042	56,858
Total liabilities	5,525,068	4,255,507
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at December 31, 2018 and 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 30,417,223 and 22,955,963 shares at December 31, 2018 and 2017, respectively	541,762	255,836
Retained earnings	303,490	255,200
Accumulated other comprehensive loss, net	(17,879)	(5,228)
Total shareholders' equity	827,373	505,808	$ 477,347	$ 452,116
Total liabilities and shareholders' equity	6,352,441	4,761,315
Parent [Member]
Assets
Cash and cash equivalents	2,374	3,924
Investment in Tri Counties Bank	880,907	557,538
Other assets	1,723	1,721
Total assets	885,004	563,183
Liabilities and shareholders' equity
Other liabilities	589	517
Junior subordinated debt	57,042	56,858
Total liabilities	57,631	57,375
Shareholders' equity:
Preferred stock, no par value: 1,000,000 shares authorized, zero issued and outstanding at December 31, 2018 and 2017
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 30,417,223 and 22,955,963 shares at December 31, 2018 and 2017, respectively	541,762	255,836
Retained earnings	303,490	255,200
Accumulated other comprehensive loss, net	(17,879)	(5,228)
Total shareholders' equity	827,373	505,808
Total liabilities and shareholders' equity	$ 885,004	$ 563,183