Fair Value Measurements - Summary of Company's Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	$ 72,558	$ 84,972
Securities available-for-sale, Gross unrealized gains	116	4
Securities available-for-sale, Gross unrealized losses	(24)	(270)
Securities available-for-sale, Estimated fair value	72,650	84,706
Trading securities, Amortized cost	73,286
Trading securities, Gross unrealized gains	409
Trading securities, Gross unrealized losses	(15)
Trading securities, Estimated fair value	73,680
Investments, Amortized cost	145,844
Investments, Gross unrealized gains	525
Investments, Gross unrealized losses	(39)
Investments, Estimated fair value	146,330	84,706
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	72,558	82,937
Securities available-for-sale, Gross unrealized gains	116	4
Securities available-for-sale, Gross unrealized losses	(24)	(270)
Securities available-for-sale, Estimated fair value	72,650	82,671
Trading securities, Amortized cost	72,119
Trading securities, Gross unrealized gains	292
Trading securities, Gross unrealized losses	(15)
Trading securities, Estimated fair value	72,396
Municipal Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost		2,035
Securities available-for-sale, Estimated fair value		$ 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	117
Trading securities, Estimated fair value	$ 1,284

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 gain in accumulated other comprehensive income (AOCI) on investments in debt and equity 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 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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