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Subsequent Event - Additional Information (Detail) - USD ($)			1 Months Ended				12 Months Ended
	Feb. 23, 2016	Feb. 02, 2016	Sep. 30, 2015	Aug. 31, 2015	Jul. 31, 2015	Feb. 28, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 22, 2014
Subsequent Event [Line Items]
Purchase of treasury shares (in shares)			81,229	198,923	114,352	341,020	735,524
Purchase of treasury shares							$ 28,823,000	$ 18,024,000	$ 13,791,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Purchase of treasury shares (in shares)	916,773
Purchase of treasury shares	$ 31,100,000
Class A Common Stock [Member]
Subsequent Event [Line Items]
Stock repurchase program, authorized amount										$ 75,000,000
Purchase of treasury shares (in shares)							735,524	501,271
Class A Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchase program expiration date		Dec. 31, 2016
Class A Common Stock [Member] | Subsequent Event [Member] | Maximum [Member]
Subsequent Event [Line Items]
Stock repurchase program, authorized amount		$ 100,000,000

X

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

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- Definition

Expiration date for the purchase of an entity's own shares under a stock repurchase plan, in the CCYY-MM-DD format.

+ References

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X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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X

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

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- Definition

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

Reference 3: 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

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