Held to Maturity Securities in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 Months, Fair Value	$ 3,754	$ 38,736
Less than 12 Months, Unrealized Losses	(4)	(88)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Fair Value	3,754	38,736
Unrealized Losses	(4)	(88)
U.S. Agency securities
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 Months, Fair Value	3,754	28,188
Less than 12 Months, Unrealized Losses	(4)	(54)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Fair Value	3,754	28,188
Unrealized Losses	(4)	(54)
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 Months, Fair Value		10,548
Less than 12 Months, Unrealized Losses		(34)
12 Months or Longer, Fair Value		0
12 Months or Longer, Unrealized Losses		0
Fair Value		10,548
Unrealized Losses		$ (34)

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 50

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

+ References

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

-Publisher FASB

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This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position.

+ References

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

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-Name Accounting Standards Codification

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for less than twelve months.

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This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

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

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This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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