Noncontrolling Interest (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 item	Mar. 31, 2014
Redeemable Noncontrolling Interest
Number of firms in which entity holds majority ownership interest	4
Fair value of noncontrolling owners equity interests	$ 37,326
Redeemable noncontrolling interest
Balance, beginning of period	39,978
Net income	553	699
Balance, end of period	37,326
Redeemable Noncontrolling Interest
Redeemable Noncontrolling Interest
Number of firms in which entity holds majority ownership interest	4
Fair value of noncontrolling owners equity interests	37,326	45,641
Redeemable noncontrolling interest
Balance, beginning of period	39,978	39,768
Net income	553	699
Distributions to redeemable noncontrolling interest	(816)	(347)
Additions and redemptions, net	(2,662)	92
Adjustments to fair value	273	5,429
Balance, end of period	$ 37,326	$ 45,641

Represents the number of consolidated investment advisory affiliates.

No definition available.

Name:	cyn_NumberOfConsolidatedInvestmentAdvisoryAffiliates
Namespace Prefix:	cyn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the net increase or decrease in redeemable noncontrolling interest from such activities as the issuance of additional equity interests to noncontrolling interest holders, the sale of a portion of the parent's controlling interest, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares by the non-wholly owned subsidiary to the parent entity, and buyback of shares by the non-wholly owned subsidiary from the noncontrolling interests.

+ References

No definition available.

+ Details

Name:	cyn_RedeemableNoncontrollingInterestIncreaseDecreaseNet
Namespace Prefix:	cyn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Change in noncontrolling interest during the period as a result of a change in the redemption value of redeemable noncontrolling interest.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestChangeInRedemptionValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Decrease in noncontrolling interest balance from payment of dividends or other distributions by the non-wholly owned subsidiary or partially owned entity, included in the consolidation of the parent entity, to the noncontrolling interest holders.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

Name:	us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_MovementInMinorityInterestRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of Net Income (Loss) attributable to redeemable noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.19)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

Name:	us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate fair value as of the reporting date of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph 14

-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph (16)(c)

-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph 15

-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph (12)(c)

-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

+ Details

Name:	us-gaap_RedeemableNoncontrollingInterestEquityFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RedeemableNoncontrollingInterestLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: