Marketable Securities - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Schedule of Available-for-sale Securities [Line Items]
Realized gains or losses recognized on sale or maturity of available-for-sale securities	$ 0	$ 0
Unrealized loss portion of securities	$ 62,897,000	$ 114,546,000
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities held in unrealized loss portion, period	12 months	12 months
UNITED STATES
Schedule of Available-for-sale Securities [Line Items]
Number of US government agency securities \| Security	2	14

Aggregate fair value of securities held in unrealized loss portion period.

No definition available.

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- Definition

Number of marketable securities held.

+ References

No definition available.

+ Details

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

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- Definition

The aggregate net change in the difference between the fair value and the carrying value, or in the comparative fair values, of marketable securities categorized as trading held at each balance sheet date, that was included in earnings for the period, which may have arisen from (a) securities classified as trading, (b) the unrealized holding gain (loss) on held-to-maturity securities transferred to the trading security category, and (c) the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) on available-for-sale securities transferred to trading securities during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27405-111563

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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