Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 66,786	$ 66,009	$ 204,836	$ 196,576
Available for sale debt securities for which a portion of an other-than-temporary impairment (OTTI) has been recorded in earnings:
Unrealized holding gains (losses) subsequent to initial OTTI recognition	5,959	(1,091)	12,245	4,572
Income tax (expense) benefit	(2,264)	415	(4,653)	(1,737)
Net unrealized gains (losses) on OTTI securities	3,695	(676)	7,592	2,835
Other available for sale investment securities:
Unrealized holding gains	40,582	53,143	75,427	78,278
Reclassification adjustment for gains included in net income	0	0	(342)	(177)
Net unrealized gains on securities	40,582	53,143	75,085	78,101
Income tax expense	(15,422)	(20,195)	(28,533)	(29,679)
Net unrealized gains on other securities	25,160	32,948	46,552	48,422
Prepaid pension cost:
Amortization of accumulated pension loss	730	821	2,190	1,901
Income tax expense	(277)	(312)	(832)	(722)
Pension loss amortization	453	509	1,358	1,179
Other comprehensive income	29,308	32,781	55,502	52,436
Comprehensive income	96,094	98,790	260,338	249,012
Non-controlling interest expense	(780)	(657)	(2,298)	(1,737)
Comprehensive income attributable to Commerce Bancshares, Inc	$ 95,314	$ 98,133	$ 258,040	$ 247,275