Business combinations - Presidio (Details)		1 Months Ended	12 Months Ended
	Oct. 11, 2019 USD ($) $ / shares shares	Oct. 31, 2019	Dec. 31, 2019 USD ($)	Dec. 19, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Assets acquired:
Securities available-for-sale			$ 45,069,000		$ 63,723,000
Securities held-to-maturity			463,000
Loans			685,964,000		336,446,000
Premises and equipment			1,756,000		350,000
Other assets, net			29,397,000		14,736,000
Liabilities assumed:
Deposits			774,259,000		416,628,000
Subordinate debt			39,554,000		39,369,000
Other borrowings			442,000		62,000
Other liabilities			17,916,000		3,038,000
Goodwill recorded in the merger			167,420,000		83,753,000	$ 45,664,000
Subordinate debt			39,554,000		$ 39,369,000
Presidio bank
Assets acquired:
Cash and cash equivalents			117,988,000
Securities available-for-sale			45,069,000
Securities held-to-maturity			463,000
Loans			685,964,000
Premises and equipment			1,756,000
Other intangible assets			11,147,000
Other assets, net			42,161,000
Total assets acquired			904,548,000
Liabilities assumed:
Deposits			774,259,000
Subordinate debt			10,000,000	$ 10,000,000
Other borrowings			442,000
Other liabilities			17,916,000
Total liabilities assumed			802,617,000
Net assets acquired			101,931,000
Purchase price			185,598,000
Goodwill recorded in the merger			$ 83,667,000
Aggregate transaction value	$ 185,598,000
Fixed exchange ratio			2.47
Issuance of shares of common stock to Presidio shareholders | shares	15,684,064
Issuance of shares of common stock to holders of restricted stock	$ 178,171,000
Stock price at Closing (in dollars per share) | $ / shares	$ 11.36
Consideration for Presidio stock options exchanged for Heritage Commerce Corp stock options	$ 7,426,000		$ 7,426,000
Cash paid for fractional shares	$ 1,000
Subordinate debt			10,000,000	$ 10,000,000
Presidio bank | Below or Above market-value lease
Liabilities assumed:
Amortized intangible assets		60 months
As Recorded | Presidio bank
Assets acquired:
Cash and cash equivalents			117,989,000
Securities available-for-sale			44,647,000
Securities held-to-maturity			463,000
Loans			698,493,000
Allowance for loan losses			(7,463,000)
Premises and equipment			1,756,000
Other assets, net			43,539,000
Total assets acquired			899,424,000
Liabilities assumed:
Deposits			774,260,000
Subordinate debt			10,000,000
Other borrowings			442,000
Other liabilities			17,916,000
Total liabilities assumed			802,618,000
Subordinate debt			10,000,000
Fair Value Adjustments | Presidio bank
Assets acquired:
Cash and cash equivalents			(1,000)
Securities available-for-sale			422,000
Loans			(12,529,000)
Allowance for loan losses			7,463,000
Other intangible assets			11,147,000
Other assets, net			(1,378,000)
Total assets acquired			5,124,000
Liabilities assumed:
Deposits			(1,000)
Total liabilities assumed			$ (1,000)