Right-Of-Use Assets and Lease Liabilities - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) lease director	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Lessee, Lease, Description [Line Items]
Number of lease contracts | lease	51
Number of operating lease agreements | lease	48
Number of financing leases | lease	3
Operating lease expense	$ 4,221	$ 3,850	$ 3,980
Related party, lease with S&T Director
Lessee, Lease, Description [Line Items]
Number of directors | director	1
Operating lease expense	$ 200
Operating lease expense		$ 200	$ 200
DNB
Lessee, Lease, Description [Line Items]
ROU asset acquired from DNB merger	$ 10,900