Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Recorded Basis	$ 20,930us-gaap_MarketableSecuritiesNoncurrent	$ 5,909us-gaap_MarketableSecuritiesNoncurrent
Recorded Basis	29,957us-gaap_MarketableSecuritiesCurrent	19,787us-gaap_MarketableSecuritiesCurrent
Current Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	30,000	19,800
Gross Unrealized Gains (Losses)	(43)	(13)
Recorded Basis	29,957	19,787
Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	20,940	5,953
Gross Unrealized Gains (Losses)	(10)	(44)
Recorded Basis	20,930	5,909
Municipal Bonds [Member] \| Long-Term Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,843	4,074
Gross Unrealized Gains (Losses)	7	(17)
Recorded Basis	3,850	4,057
Corporate Bonds [Member] \| Current Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	9,800
Gross Unrealized Gains (Losses)	0	(13)
Recorded Basis	0	9,787
Corporate Bonds [Member] \| Long-Term Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	2,153	1,879
Gross Unrealized Gains (Losses)	(3)	(27)
Recorded Basis	2,150	1,852
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	10,000
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	21,670	10,000
Certificate of Deposits [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	14,944	0
Gross Unrealized Gains (Losses)	(14)	0
Recorded Basis	14,930	0
Certificate of Deposits [Member] \| Current Available-for-Sale [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	8,330	0
Gross Unrealized Gains (Losses)	(43)	0
Recorded Basis	$ 8,287	$ 0

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.

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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

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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

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-Article 5

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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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