Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Recorded Basis	$ 15,984	$ 5,909
Recorded Basis	34,760	19,787
Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	16,020	5,953
Gross Unrealized (Losses) Gains	(36)	(44)
Recorded Basis	15,984	5,909
Corporate Bonds [Member] \| Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	12,006	1,879
Gross Unrealized (Losses) Gains	(49)	(27)
Recorded Basis	11,957	1,852
Fair Value Category	2
Municipal Bonds [Member] \| Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	4,014	4,074
Gross Unrealized (Losses) Gains	13	(17)
Recorded Basis	4,027	4,057
Fair Value Category	2
Current Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	34,775	19,800
Gross Unrealized (Losses) Gains	(15)	(13)
Recorded Basis	34,760	19,787
Current Available-for-Sale [Member] \| Variable Rate Demand Notes (VRDN) [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	21,790	10,000
Gross Unrealized (Losses) Gains	0	0
Recorded Basis	21,790	10,000
Fair Value Category	2
Current Available-for-Sale [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	12,985	9,800
Gross Unrealized (Losses) Gains	(15)	(13)
Recorded Basis	$ 12,970	$ 9,787
Fair Value Category	2

Fair value category.

No definition available.

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- Definition

Marketable securities unrealized holding gain loss.

+ References

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

-Section 25

-Paragraph 1

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-Section 50

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-Topic 942

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-Section 50

-Paragraph 2

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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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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 2

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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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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