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Fair Value Measurement - Summary of Marketable Securities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost $ 289,132 $ 301,170
Gross Unrealized Gains (Losses) 15 (52)
Recorded Basis 289,147 301,118
Marketable Securities Current [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 78,105 107,335
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 78,105 107,335
Marketable Securities Current [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 38,056 21,312
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 38,056 21,312
Marketable Securities Current [Member] | Available For Sale Restricted [Member] | Money Market Funds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 40,049 76,023
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 40,049 76,023
Marketable Securities Current [Member] | Available For Sale Restricted [Member] | Certificate 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 211,027 193,835
Gross Unrealized Gains (Losses) 15 (52)
Recorded Basis 211,042 193,783
Marketable Securities Noncurrent [Member] | Available-for-sale Securities [Member] | Money Market Funds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 78 4
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 78 4
Marketable Securities Noncurrent [Member] | Available-for-sale Securities [Member] | Municipal Bonds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 3,064 3,135
Gross Unrealized Gains (Losses) 11 (3)
Recorded Basis 3,075 3,132
Marketable Securities Noncurrent [Member] | Available-for-sale Securities [Member] | Corporate Bonds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 3,070 2,970
Gross Unrealized Gains (Losses) (9) (24)
Recorded Basis 3,061 2,946
Marketable Securities Noncurrent [Member] | Available For Sale Restricted [Member] | Money Market Funds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 180,253 175,869
Gross Unrealized Gains (Losses) 0 0
Recorded Basis 180,253 175,869
Marketable Securities Noncurrent [Member] | Available For Sale Restricted [Member] | Certificate of Deposit [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 11,776 496
Gross Unrealized Gains (Losses) (2) (1)
Recorded Basis 11,774 495
Marketable Securities Noncurrent [Member] | Available For Sale Restricted [Member] | Municipal Bonds [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 3,421 3,613
Gross Unrealized Gains (Losses) 11 (1)
Recorded Basis 3,432 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) (10) (24)
Recorded Basis 3,207 2,972
Marketable Securities Noncurrent [Member] | Available For Sale Restricted [Member] | U.S. Treasuries [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 6,148 4,752
Gross Unrealized Gains (Losses) 14 1
Recorded Basis $ 6,162 $ 4,753