Fair Value Measurements - Summary of Company's Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	$ 72,701	$ 84,972
Securities available-for-sale, Gross unrealized gains	92	4
Securities available-for-sale, Gross unrealized losses	(55)	(270)
Securities available-for-sale, Estimated fair value	72,738	84,706
Trading securities, Amortized cost	74,265
Trading securities, Gross unrealized gains	242
Trading securities, Gross unrealized losses	(19)
Trading securities, Estimated fair value	74,488
Investments, Amortized cost	146,966
Investments, Gross unrealized gains	334
Investments, Gross unrealized losses	(74)
Investments, Estimated fair value	147,226	84,706
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	70,690	82,937
Securities available-for-sale, Gross unrealized gains	92	4
Securities available-for-sale, Gross unrealized losses	(55)	(270)
Securities available-for-sale, Estimated fair value	70,727	82,671
Trading securities, Amortized cost	73,098
Trading securities, Gross unrealized gains	156
Trading securities, Gross unrealized losses	(19)
Trading securities, Estimated fair value	73,235
Municipal Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	2,011	2,035
Securities available-for-sale, Estimated fair value	2,011	$ 2,035
Mutual Funds Held In Rabbi Trust [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	1,167
Trading securities, Gross unrealized gains	86
Trading securities, Estimated fair value	$ 1,253

Marketable securities accumulated gross unrealized gain before tax.

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Marketable securities accumulated gross unrealized loss before tax.

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Marketable securities amortized cost.

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Trading securities accumulated gross unrealized gain before tax.

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Trading securities accumulated gross unrealized loss before tax.

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

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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.

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Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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