Summary Of Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 129,801		$ 127,575		$ 120,549		$ 119,144		$ 108,841		$ 90,303		$ 87,786		$ 87,816		$ 497,069		$ 374,746		$ 337,969
Total interest expense	5,913		4,779		3,875		3,663		2,617		1,374		1,625		1,141		18,230		6,757		4,350
Net Interest Income	123,888		122,796		116,674		115,481		106,224		88,929		86,161		86,675		478,839		367,989		333,619
Provision for loan and lease losses	1,789		3,153		3,975		5,852		3,327		(648)		3,177		2,775		14,769		8,631		10,778
Noninterest income	20,402		21,019		23,692		23,143		23,581		37,067		24,135		24,859		88,256		109,642		88,082
Noninterest expense	87,019		82,841		84,643		85,987		85,627		67,537		68,867		68,986		340,490		291,017		261,142
Income before income taxes	55,482		57,821		51,748		46,785		40,851		59,107		38,252		39,773		211,836		177,983		149,781
Provision for income taxes	10,734		11,406		9,999		6,815		25,123		18,338		11,120		10,574		38,954		65,155		44,915
Net income	$ 44,748		$ 46,415		$ 41,749		$ 39,970		$ 15,728		$ 40,769		$ 27,132		$ 29,199		$ 172,882		$ 112,828		$ 104,866
Per Common Share
Earnings (basic)	$ 0.61	[3]	$ 0.63	[3]	$ 0.57	[3]	$ 0.55	[3]	$ 0.23	[3]	$ 0.70	[3]	$ 0.47	[3]	$ 0.50	[3]	$ 2.36	[3]	$ 1.86	[3]	$ 1.81
Earnings (diluted)	$ 0.61	[3]	$ 0.63	[3]	$ 0.57	[3]	$ 0.55	[3]	$ 0.23	[3]	$ 0.70	[3]	$ 0.47	[3]	$ 0.50	[3]	$ 2.36	[3]	$ 1.86	[3]	$ 1.81

[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.

[3] Due to averaging of shares, quarterly earnings per share may not add up to the totals reported for the full year.