The Business of Sierra Bancorp (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) store	Dec. 31, 2018 USD ($)	Jan. 31, 1978 USD ($) store
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of branches | store			1
Capital | $			$ 1,500
Number of acquired banks | store	4
Number of full service branch offices | store	40
Assets | $	$ 2,635,960	$ 2,522,502
Cash, FDIC Insured Amount | $	$ 2,200,000