TriCo Bancshares Condensed Financial Statements (Parent Only) - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Assets
Cash and Cash equivalents	$ 188,034	$ 305,612	$ 315,088	$ 303,461
Other assets	86,936	74,743
Total assets	4,656,435	4,517,968
Liabilities and shareholders' equity
Other liabilities	62,850	67,364
Junior subordinated debt	56,810	56,667
Total liabilities	4,149,702	4,040,621
Shareholders' equity:
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 22,941,464 and 22,867,802 shares, respectively	255,231	252,820
Retained earnings	256,114	232,440
Accumulated other comprehensive loss, net	(4,612)	(7,913)
Total shareholders' equity	506,733	477,347	481,890	452,116
Total liabilities and shareholders' equity	4,656,435	4,517,968
Parent [Member]
Assets
Cash and Cash equivalents	3,278	2,802	$ 2,768	$ 2,565
Investment in Tri Counties Bank	558,986	529,907
Other assets	1,729	1,711
Total assets	563,993	534,420
Liabilities and shareholders' equity
Other liabilities	450	406
Junior subordinated debt	56,810	56,667
Total liabilities	57,260	57,073
Shareholders' equity:
Common stock, no par value: authorized 50,000,000 shares; issued and outstanding 22,941,464 and 22,867,802 shares, respectively	255,231	252,820
Retained earnings	256,114	232,440
Accumulated other comprehensive loss, net	(4,612)	(7,913)
Total shareholders' equity	506,733	477,347
Total liabilities and shareholders' equity	$ 563,993	$ 534,420