Securities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Available-for-Sale [Abstract]
Amortized Cost	$ 635,133,000		$ 635,133,000		$ 621,753,000
Gross Unrealized Gains	6,963,000		6,963,000		6,457,000
Gross Unrealized Losses	(8,524,000)		(8,524,000)		(18,805,000)
Fair Value	633,572,000		633,572,000		609,405,000
Available-for-sale Equity Securities [Abstract]
Amortized Cost	25,000,000		25,000,000		55,000,000
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(319,000)		(319,000)		(2,218,000)
Fair Value	24,681,000		24,681,000		52,782,000
Available-for-sale Debt Securities [Abstract]
Amortized Cost	610,133,000		610,133,000		566,753,000
Gross Unrealized Gains	6,963,000		6,963,000		6,457,000
Gross Unrealized Losses	(8,205,000)		(8,205,000)		(16,587,000)
Fair Value	608,891,000		608,891,000		556,623,000
Held-to-Maturity [Abstract]
Amortized Cost	1,662,000		1,662,000		1,662,000
Gross Unrealized Gains	1,000		1,000		1,000
Gross Unrealized Losses	(32,000)		(32,000)		(62,000)
Fair Value	1,631,000		1,631,000		1,601,000
Available-for-Sale, Amortized Cost [Abstract]
Due in one year or less	3,371,000		3,371,000
Due after one through five years	108,097,000		108,097,000
Due after five through ten years	129,882,000		129,882,000
Due after ten years	33,143,000		33,143,000
U.S. government sponsored agency mortgage-backed securities	335,640,000		335,640,000
Amortized Cost	610,133,000		610,133,000		566,753,000
Marketable equity securities	25,000,000		25,000,000		55,000,000
Amortized Cost	635,133,000		635,133,000		621,753,000
Available-for-Sale, Fair Value [Abstract]
Due in one year or less	3,400,000		3,400,000
Due after one through five years	108,713,000		108,713,000
Due after five through ten years	129,250,000		129,250,000
Due after ten years	33,735,000		33,735,000
U.S. government sponsored agency mortgage-backed securities	333,793,000		333,793,000
Total debt securities	608,891,000		608,891,000
Marketable equity securities	24,681,000		24,681,000
Total securities	633,572,000		633,572,000
Held-to-Maturity, Amortized Cost [Abstract]
Due in one year or less	0		0
Due after one through five years	0		0
Due after five through ten years	1,182,000		1,182,000
Due after ten years	480,000		480,000
U.S. government sponsored agency mortgage-backed securities	0		0
Amortized Cost	1,662,000		1,662,000		1,662,000
Marketable equity securities	0		0
Total securities	1,662,000		1,662,000
Held-to-Maturity, Fair Value [Abstract]
Due in one year or less	0		0
Due after one through five years	0		0
Due after five through ten years	1,183,000		1,183,000
Due after ten years	448,000		448,000
U.S. government sponsored agency mortgage-backed securities	0		0
Total debt securities	1,631,000		1,631,000		1,601,000
Marketable equity securities	0		0
Total securities	1,631,000		1,631,000
Securities gains (loss), net	(34,000)	(23,000)	(145,000)	(31,000)
Realized pre-tax gain on sale of securities			1,800,000	0
Realized pre-tax loss on sale of securities			2,000,000	0
Securities pledged as collateral to secure public deposit and for other purposes	237,700,000		237,700,000		257,500,000
Amortized cost of securities sold under agreements to repurchase	264,500,000		264,500,000		255,400,000
Percentage of total investment with unrealized losses (in hundredths)	57.80%		57.80%		67.80%
CTBI fixed income mutual funds of total fair value			24,700,000
CTBI fixed income mutual funds of total unrealized losses			319,000
Percentage Severity of the impairment in fair value less than cost (in hundredths)	1.30%		1.30%
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	160,071,000		160,071,000		382,620,000
12 Months or More	215,420,000		215,420,000		49,968,000
Total	375,491,000		375,491,000		432,588,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	(942,000)		(942,000)		(14,806,000)
12 Months or More	(7,582,000)		(7,582,000)		(3,999,000)
Total	(8,524,000)		(8,524,000)		(18,805,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	159,129,000		159,129,000		367,814,000
12 Months or More	207,838,000		207,838,000		45,969,000
Total	366,967,000		366,967,000		413,783,000
Held-to-Maturity, Amortized Cost [Abstract]
12 Months or More	480,000		480,000		480,000
Held-to-Maturity, Gross Unrealized Losses [Abstract]
12 Months or More	(32,000)		(32,000)		(62,000)
Held-to-Maturity, Fair Value [Abstract]
12 Months or More	448,000		448,000		418,000
U.S. Treasury and government agencies [Member]
Available-for-sale Debt Securities [Abstract]
Amortized Cost	140,853,000		140,853,000		65,524,000
Gross Unrealized Gains	261,000		261,000		225,000
Gross Unrealized Losses	(2,706,000)		(2,706,000)		(5,139,000)
Fair Value	138,408,000		138,408,000		60,610,000
Held-to-Maturity [Abstract]
Amortized Cost	480,000		480,000		480,000
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(32,000)		(32,000)		(62,000)
Fair Value	448,000		448,000		418,000
Available-for-Sale, Amortized Cost [Abstract]
Amortized Cost	140,853,000		140,853,000		65,524,000
Held-to-Maturity, Amortized Cost [Abstract]
Amortized Cost	480,000		480,000		480,000
Held-to-Maturity, Fair Value [Abstract]
Total debt securities	448,000		448,000		418,000
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	56,052,000		56,052,000		21,750,000
12 Months or More	55,519,000		55,519,000		35,750,000
Total	111,571,000		111,571,000		57,500,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	(103,000)		(103,000)		(1,617,000)
12 Months or More	(2,603,000)		(2,603,000)		(3,522,000)
Total	(2,706,000)		(2,706,000)		(5,139,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	55,949,000		55,949,000		20,133,000
12 Months or More	52,916,000		52,916,000		32,228,000
Total	108,865,000		108,865,000		52,361,000
Held-to-Maturity, Amortized Cost [Abstract]
12 Months or More	480,000		480,000		480,000
Held-to-Maturity, Gross Unrealized Losses [Abstract]
12 Months or More	(32,000)		(32,000)		(62,000)
Held-to-Maturity, Fair Value [Abstract]
12 Months or More	448,000		448,000		418,000
State and political subdivisions [Member]
Available-for-sale Debt Securities [Abstract]
Amortized Cost	133,640,000		133,640,000		118,055,000
Gross Unrealized Gains	3,768,000		3,768,000		1,907,000
Gross Unrealized Losses	(718,000)		(718,000)		(3,259,000)
Fair Value	136,690,000		136,690,000		116,703,000
Held-to-Maturity [Abstract]
Amortized Cost	1,182,000		1,182,000		1,182,000
Gross Unrealized Gains	1,000		1,000		1,000
Gross Unrealized Losses	0		0		0
Fair Value	1,183,000		1,183,000		1,183,000
Available-for-Sale, Amortized Cost [Abstract]
Amortized Cost	133,640,000		133,640,000		118,055,000
Held-to-Maturity, Amortized Cost [Abstract]
Amortized Cost	1,182,000		1,182,000		1,182,000
Held-to-Maturity, Fair Value [Abstract]
Total debt securities	1,183,000		1,183,000		1,183,000
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	6,305,000		6,305,000		57,165,000
12 Months or More	25,528,000		25,528,000		7,639,000
Total	31,833,000		31,833,000		64,804,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	(30,000)		(30,000)		(2,789,000)
12 Months or More	(688,000)		(688,000)		(470,000)
Total	(718,000)		(718,000)		(3,259,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	6,275,000		6,275,000		54,376,000
12 Months or More	24,840,000		24,840,000		7,169,000
Total	31,115,000		31,115,000		61,545,000
U.S. government sponsored agency mortgage-backed securities [Member]
Available-for-sale Debt Securities [Abstract]
Amortized Cost	335,640,000		335,640,000		383,174,000
Gross Unrealized Gains	2,934,000		2,934,000		4,325,000
Gross Unrealized Losses	(4,781,000)		(4,781,000)		(8,189,000)
Fair Value	333,793,000		333,793,000		379,310,000
Available-for-Sale, Amortized Cost [Abstract]
Amortized Cost	335,640,000		335,640,000		383,174,000
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	97,714,000		97,714,000		248,705,000
12 Months or More	109,373,000		109,373,000		6,579,000
Total	207,087,000		207,087,000		255,284,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	(809,000)		(809,000)		(8,182,000)
12 Months or More	(3,972,000)		(3,972,000)		(7,000)
Total	(4,781,000)		(4,781,000)		(8,189,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	96,905,000		96,905,000		240,523,000
12 Months or More	105,401,000		105,401,000		6,572,000
Total	202,306,000		202,306,000		247,095,000
Debt securities [Member]
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	160,071,000		160,071,000		327,620,000
12 Months or More	190,420,000		190,420,000
Total	350,491,000		350,491,000		377,588,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	(942,000)		(942,000)		(12,588,000)
12 Months or More	(7,263,000)		(7,263,000)
Total	(8,205,000)		(8,205,000)		(16,587,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	159,129,000		159,129,000		315,032,000
12 Months or More	183,157,000		183,157,000
Total	342,286,000		342,286,000		361,001,000
Marketable equity securities [Member]
Available-for-Sale, Amortized Cost [Abstract]
Less Than 12 Months	0		0		55,000,000
12 Months or More	25,000,000		25,000,000
Total	25,000,000		25,000,000		55,000,000
Available-for-Sale, Gross Unrealized Losses [Abstract]
Less Than 12 Months	0		0		(2,218,000)
12 Months or More	(319,000)		(319,000)
Total	(319,000)		(319,000)		(2,218,000)
Available-for-Sale, Fair Value [Abstract]
Less Than 12 Months	0		0		52,782,000
12 Months or More	24,681,000		24,681,000
Total	$ 24,681,000		$ 24,681,000		$ 52,782,000