Outstanding Debt Consisted (Parenthetical) (Detail) - 7.75% Subordinated Notes due 2045	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Subordinated Notes percentage	7.75%	7.75%
Subordinated Notes due date	2045	2045

Contractual interest rate for funds borrowed, under the debt agreement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant