Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	[2]	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Deposit account and treasury management fees											$ 36,072	$ 30,381	$ 28,500
Card revenue											19,719	25,627	23,620
Financial services and trust revenue											12,135	11,478	11,266
Revenue from contracts with customers											67,926
Noninterest income, excluding revenue from contracts with customers											20,330
Noninterest income	$ 20,402	$ 21,019	$ 23,692	$ 23,143	$ 23,581		$ 37,067		$ 24,135	$ 24,859	$ 88,256	$ 109,642	$ 88,082

[1] During the fourth quarter of 2017, Columbia acquired Pacific Continental and also recorded a charge through provision for income taxes related to the re-measurement of our deferred tax assets pursuant to the newly enacted Tax Cuts and Jobs Act. See Note 2, “Business Combinations,” for further information regarding this acquisition. See Note 23, “Income Tax,” for further information regarding the re-measurement of our deferred tax assets.

[2] During the third quarter of 2017, Columbia sold its merchant card services portfolio.