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Investments - Securities and Investments, Recorded at Either Fair Value or Cost (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 195,549 | $ 190,146
Gross Unrealized Gains | 4,156 | 2,709
Gross Unrealized Losses | (1,368) | (2,132)
Available-for-sale-securities, Carrying Value | 198,337 | 190,723
Restricted investment held at cost | 27,800 | 27,800
Other investments held at cost | 734 | 767
Total carrying value of available-for-sale investments | 226,871 | 219,290
Deferred Compensation Plan Assets [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 15,084 | 12,367
Gross Unrealized Gains | 2,314 | 2,271
Gross Unrealized Losses | (26) | (42)
Available-for-sale-securities, Carrying Value | 17,372 | 14,596
Corporate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 72,324 | 66,522
Gross Unrealized Gains | 99 | 64
Gross Unrealized Losses | (150) | (174)
Available-for-sale-securities, Carrying Value | 72,273 | 66,412
Municipal Fixed-Rate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 10,970 | 11,799
Gross Unrealized Gains | 14 | 12
Gross Unrealized Losses | (25) | (37)
Available-for-sale-securities, Carrying Value | 10,959 | 11,774
Asset-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 11,832 | 10,201
Gross Unrealized Gains | 10 | 19
Gross Unrealized Losses | (14) | (14)
Available-for-sale-securities, Carrying Value | 11,828 | 10,206
Mortgage/Agency-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 12,370 | 13,080
Gross Unrealized Gains | 23 | 15
Gross Unrealized Losses | (80) | (91)
Available-for-sale-securities, Carrying Value | 12,313 | 13,004
U.S. Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 28,251 | 30,022
Gross Unrealized Gains | 27 | 15
Gross Unrealized Losses | (231) | (270)
Available-for-sale-securities, Carrying Value | 28,047 | 29,767
Foreign Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 3,279 | 3,729
Gross Unrealized Gains |  | 2
Gross Unrealized Losses |  | (1)
Available-for-sale-securities, Carrying Value | 3,279 | 3,730
Variable Rate Demand Notes [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 10,505 | 11,855
Available-for-sale-securities, Carrying Value | 10,505 | 11,855
Marketable Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 30,934 | 30,571
Gross Unrealized Gains | 1,669 | 311
Gross Unrealized Losses | (842) | (1,503)
Available-for-sale-securities, Carrying Value | $ 31,761 | $ 29,379

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- 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 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562 + Details
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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=73527792&loc=d3e27161-111563 + Details
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