Investments - Schedule of Additional Information about Investments in Unrealized Loss Position (Detail)	Mar. 31, 2015 Issue	Dec. 31, 2014 Issue
Number of issues (Cusip numbers) held:
Less than Twelve Months	99	80
Twelve Months or Longer	63	173
Number of issues (Cusip numbers) held, Total	162	253

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant