Short-Term Borrowings and Long-Term Debt Subordinated Debt (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($)	Dec. 31, 2021 USD ($) subsidiarytrusts	Mar. 31, 2020 USD ($)	Mar. 31, 2017 USD ($)	Nov. 30, 2014 USD ($)
Subordinated Debt [Abstract]
Subsidiary trusts owned by parent | subsidiarytrusts		3
Subordinated debt
Subordinated Debt [Abstract]
Debt instrument, face amount	$ 150,000,000
Effective interest rate	4.69%
Interest Rate	4.50%
Subordinated debt | 3.25% Notes due 2030
Subordinated Debt [Abstract]
Debt instrument, face amount			$ 200,000,000
Stated interest rate			3.25%
Effective interest rate			3.35%
Subordinated debt | 3.75% Notes due 2035
Subordinated Debt [Abstract]
Debt instrument, face amount			$ 175,000,000
Stated interest rate			3.75%
Effective interest rate			3.85%
Subordinated debt | November 2024 Subordinated Debt
Subordinated Debt [Abstract]
Stated interest rate					4.50%
Effective interest rate					4.87%
Subordinated debt					$ 100,000,000
Senior Notes
Subordinated Debt [Abstract]
Debt instrument, face amount				$ 125,000,000
Stated interest rate				3.60%
Effective interest rate				3.95%
Junior subordinated deferrable interest debentures
Subordinated Debt [Abstract]
Subordinated debt		$ 16,496,000
Junior subordinated deferrable interest debentures | Columbia Bancorp Statutory Trust
Subordinated Debt [Abstract]
Interest Rate		2.78%
Subordinated debt		$ 6,186,000
Call Price		1.000
Junior subordinated deferrable interest debentures | Columbia Bancorp Statutory Trust II
Subordinated Debt [Abstract]
Interest Rate		2.09%
Subordinated debt		$ 4,124,000
Call Price		1.000
Junior subordinated deferrable interest debentures | Columbia Bancorp Statutory Trust III
Subordinated Debt [Abstract]
Interest Rate		1.97%
Subordinated debt		$ 6,186,000
Call Price		1.000