Financial Instruments - Summary of Bond Activity (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value at beginning of period	$ 38,399	$ 30,011
Purchases	6,661	14,089
Sales		(245)
Maturities and calls	(5,950)	(6,426)
Increase in bond premium	59	1,155
Fair market value adjustment	(12)	(185)
Fair value at end of period	$ 39,157	$ 38,399

The fair value as of the balance sheet date of firm holdings in fixed income or other debt securities issued by a corporation or other issuer not elsewhere specified in the taxonomy. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

Name:	us-gaap_FinancialInstrumentsOwnedCorporateDebtAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant