Fair Value Measurement - Summary of Marketable Securities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	$ 300,819	$ 301,170
Gross Unrealized Gains (Losses)	35	(52)
Recorded Basis	300,854	301,118
Marketable Securities Current [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	53,201	107,335
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	53,201	107,335
Marketable Securities Current [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	4,830	21,312
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	4,830	21,312
Marketable Securities Current [Member] \| Available For Sale Restricted [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	48,371	76,023
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	48,371	76,023
Marketable Securities Current [Member] \| Available For Sale Restricted [Member] \| Certificates of Deposit [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	10,000
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	0	10,000
Marketable Securities Noncurrent [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	247,618	193,835
Gross Unrealized Gains (Losses)	35	(52)
Recorded Basis	247,653	193,783
Marketable Securities Noncurrent [Member] \| Available-for-sale Securities [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	94	4
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	94	4
Marketable Securities Noncurrent [Member] \| Available-for-sale Securities [Member] \| Municipal Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	1,500	3,135
Gross Unrealized Gains (Losses)	1	(3)
Recorded Basis	1,501	3,132
Marketable Securities Noncurrent [Member] \| Available-for-sale Securities [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	863	2,970
Gross Unrealized Gains (Losses)	(2)	(24)
Recorded Basis	861	2,946
Marketable Securities Noncurrent [Member] \| Available For Sale Restricted [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	221,728	175,869
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	221,728	175,869
Marketable Securities Noncurrent [Member] \| Available For Sale Restricted [Member] \| Certificates of Deposit [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	11,776	496
Gross Unrealized Gains (Losses)	(1)	(1)
Recorded Basis	11,775	495
Marketable Securities Noncurrent [Member] \| Available For Sale Restricted [Member] \| Municipal Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,160	3,613
Gross Unrealized Gains (Losses)	12	(1)
Recorded Basis	3,172	3,612
Marketable Securities Noncurrent [Member] \| Available For Sale Restricted [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,217	2,996
Gross Unrealized Gains (Losses)	8	(24)
Recorded Basis	3,225	2,972
Marketable Securities Noncurrent [Member] \| Available For Sale Restricted [Member] \| U.S. Treasuries [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	5,280	4,752
Gross Unrealized Gains (Losses)	17	1
Recorded Basis	$ 5,297	$ 4,753

This item represents the cost of debt 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 2: 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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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.

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Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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