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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 155,253	$ 189,538
Investments, Gross Unrealized Gains	122	35
Investments, Gross Unrealized (Losses)	(76)	(110)
Investments, Estimated Fair Value	155,299	189,463
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3,479	23,818
Investments, Estimated Fair Value	3,479	23,818
Bankers Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,117	1,439
Investments, Estimated Fair Value	1,117	1,439
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	36,711	36,847
Investments, Gross Unrealized Gains	12	6
Investments, Gross Unrealized (Losses)	(41)	(44)
Investments, Estimated Fair Value	36,682	36,809
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	12,160	24,423
Investments, Gross Unrealized (Losses)	(26)	(42)
Investments, Estimated Fair Value	12,134	24,381
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	51,328	46,700
Investments, Gross Unrealized Gains	70	21
Investments, Gross Unrealized (Losses)	(5)	(14)
Investments, Estimated Fair Value	51,393	46,707
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	251	591
Investments, Estimated Fair Value	251	591
Promissory Note [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	675	675
Investments, Estimated Fair Value	675	675
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	20,418	25,414
Investments, Gross Unrealized Gains	6
Investments, Estimated Fair Value	20,424	25,414
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	29,114	29,631
Investments, Gross Unrealized Gains	34	8
Investments, Gross Unrealized (Losses)	(4)	(10)
Investments, Estimated Fair Value	29,144	29,629
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	6,497	6,276
Investments, Gross Unrealized (Losses)	(864)	(718)
Investments, Estimated Fair Value	$ 5,633	$ 5,558

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
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