v3.8.0.1

Investments - Components of Investments (Detail) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | $ 219,351 | $ 305,915
Unrealized Gains | 3 | 2
Unrealized Losses | (307) | (693)
Fair Value | 219,047 | 305,224
Investment Type [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 216,721 | 303,521
Unrealized Gains | 3 | 2
Unrealized Losses | (307) | (693)
Fair Value | 216,417 | 302,830
Investment Type [Member] | Money Market Mutual Funds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 5,278 | 18,118
Fair Value | 5,278 | 18,118
Investment Type [Member] | Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 9,423 | 27,906
Unrealized Losses | (10) | (39)
Fair Value | 9,413 | 27,867
Investment Type [Member] | US Government Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 13,505 | 13,295
Unrealized Losses | (14) | (32)
Fair Value | 13,491 | 13,263
Investment Type [Member] | Corporate Bonds and Notes [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 188,515 | 244,202
Unrealized Gains | 3 | 2
Unrealized Losses | (283) | (622)
Fair Value | 188,235 | 243,582
Deferred Compensation Plan Assets [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cost Basis | 2,630 | 2,394
Fair Value | $ 2,630 | $ 2,394

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- Definition 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 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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