Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Recorded Basis	$ 6,034us-gaap_MarketableSecuritiesNoncurrent	$ 20,930us-gaap_MarketableSecuritiesNoncurrent
Recorded Basis	21,670us-gaap_MarketableSecuritiesCurrent	29,957us-gaap_MarketableSecuritiesCurrent
Current Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	21,670	30,000
Gross Unrealized (Losses) Gains	0	(43)
Recorded Basis	21,670	29,957
Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	6,019	20,940
Gross Unrealized (Losses) Gains	15	(10)
Recorded Basis	6,034	20,930
Municipal Bonds [Member] \| Long-Term Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,547	3,843
Gross Unrealized (Losses) Gains	14	7
Recorded Basis	3,561	3,850
Corporate Bonds [Member] \| Long-Term Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	2,472	2,153
Gross Unrealized (Losses) Gains	1	(3)
Recorded Basis	2,473	2,150
Variable Rate Demand Notes (VRDN) [Member] \| Current Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	21,670	21,670
Gross Unrealized (Losses) Gains	0	0
Recorded Basis	21,670	21,670
Certificate of Deposit [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	14,944
Gross Unrealized (Losses) Gains	0	(14)
Recorded Basis	0	14,930
Certificate of Deposit [Member] \| Current Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	8,330
Gross Unrealized (Losses) Gains	0	(43)
Recorded Basis	$ 0	$ 8,287

Marketable securities unrealized holding gain loss.

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity 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.

+ References

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- Definition

Amount of debt 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

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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-Name Regulation S-X (SX)

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-Section 02

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-Article 5

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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity and (2) securities available-for-sale that will be held for the long-term.

+ References

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