Acquisition - Narrative (Details) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2015 USD ($) community Office $ / shares shares	Sep. 30, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares
Business Acquisition [Line Items]
Common stock, par value | $ / shares	$ 5		$ 5	$ 5
Deposits			$ 2,394,360	$ 1,861,341
Interest component of expected cash flows (accretable difference)			144	$ 0
Fox Chase Bank [Member]
Business Acquisition [Line Items]
Integration and acquisition-related costs, gross			540
Fox Chase Bank [Member] | Scenario, Forecast [Member]
Business Acquisition [Line Items]
Total purchase price		$ 239,300
Assets acquired		1,100,000
Loans acquired		767,700
Deposits acquired		$ 765,000
Cash paid per share at acquisition | $ / shares		$ 21.00
Number of shares per common stock, exchange ratio		97.31%
Allocation provision, cash consideration		40.00%
Allocation provision, stock consideration		60.00%
Valley Green Bank [Member]
Business Acquisition [Line Items]
Total purchase price	$ 78,906
Assets acquired	425,185
Loans acquired	$ 1,813
Number of banking offices operated in greater Philadelphia marketplace (in offices) | community	3
Number of loan production offices in Philadelphia marketplace | Office	2
Merger agreement aggregate value	$ 77,000
Exchange ratio	135.41%
Univest shares issued | shares	3,787,866
Outstanding stock options prior to exchange | shares	122,377
Cash and related payroll taxes exchanged for employee stock options	$ 2,200
Purchase price assigned to cash in lieu of fractional shares	3
Loans held for investment	380,924
Deposits	385,900
Loans receivable without evidence of credit quality deterioration, current fair value	379,200
Fair value premium	4,400
Fair value discount	$ 5,500
Fair value adjustment, period of amortization	10 years
Acquired impaired loans	$ 1,700
Contractual cash flows not expected to be collected (nonaccretable difference)	5,344
Interest component of expected cash flows (accretable difference)	305
Customer related intangibles	$ 1,520
Useful life of intangible asset	10 years
Fair value premium	$ 686
Integration and acquisition-related costs, gross			$ 2,000