Fair Value Measurement - Summary of Restricted Marketable Securities Component and Workers' Compensation Deposits (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	$ 6,045	$ 20,940
Long-Term Available-for-Sale [Member] \| Municipal Bonds [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,438	3,843
Long-Term Available-for-Sale [Member] \| Corporate Bonds [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	2,607	2,153
Long-Term Restricted Marketable Securities [Member] \| Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	101,187	58,165
Gross Unrealized Gains (Losses)	6	18
Recorded Basis	101,193	58,183
Long-Term Restricted Marketable Securities [Member] \| Long-Term Available-for-Sale [Member] \| Money Market Funds Held in Trust [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	88,153	46,310
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	88,153	46,310
Long-Term Restricted Marketable Securities [Member] \| Long-Term Available-for-Sale [Member] \| Municipal Bonds [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,952	4,352
Gross Unrealized Gains (Losses)	10	21
Recorded Basis	3,962	4,373
Long-Term Restricted Marketable Securities [Member] \| Long-Term Available-for-Sale [Member] \| Corporate Bonds [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	4,002	3,540
Gross Unrealized Gains (Losses)	(4)	(3)
Recorded Basis	3,998	3,537
Long-Term Restricted Marketable Securities [Member] \| Long-Term Available-for-Sale [Member] \| U.S. Treasuries [Member] \| Level 1 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	5,080	3,963
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	5,080	3,963
Long-Term Restricted Marketable Securities [Member] \| Current Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	21,343	3,776
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	21,343	3,776
Long-Term Restricted Marketable Securities [Member] \| Current Available-for-Sale [Member] \| Money Market Funds Held in Trust [Member] \| Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	21,343	3,776
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	$ 21,343	$ 3,776

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 unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (d)

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Investments in debt and equity securities which are categorized neither as trading securities nor held-to-maturity securities, which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer, and that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.

+ 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)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB

-Name Accounting Standards Codification

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-Section 25

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(b))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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-Publisher FASB

-Name Accounting Standards Codification

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-Section 25

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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