Investments - Debt Securities and Other Investments, Recorded at Either Fair Value or Cost (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 89,693	$ 62,857
Gross Unrealized Gains	59	53
Gross Unrealized Losses	(684)	(417)
Available-for-sale debt securities, Carrying Value	89,068	62,493
Restricted investment held at cost	26,700	27,800
Other investments held at cost	520	547
Total carrying value of available-for-sale investments	116,288	90,840
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,109	32,654
Gross Unrealized Gains	43	44
Gross Unrealized Losses	(333)	(155)
Available-for-sale debt securities, Carrying Value	48,819	32,543
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,413	2,902
Gross Unrealized Gains		2
Gross Unrealized Losses	(30)	(22)
Available-for-sale debt securities, Carrying Value	2,383	2,882
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,334	6,545
Gross Unrealized Gains		1
Gross Unrealized Losses	(44)	(20)
Available-for-sale debt securities, Carrying Value	13,290	6,526
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,906	5,554
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(72)	(46)
Available-for-sale debt securities, Carrying Value	8,836	5,509
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,703	14,477
Gross Unrealized Gains	10
Gross Unrealized Losses	(204)	(174)
Available-for-sale debt securities, Carrying Value	14,509	14,303
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,228	725
Gross Unrealized Gains	4	5
Gross Unrealized Losses	(1)
Available-for-sale debt securities, Carrying Value	$ 1,231	$ 730

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

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

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB
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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Amount of investments classified as other.

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Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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