Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Details)

v3.6.0.2
Summary of Significant Accounting Policies - Additional Information (Details)
 12 Months Ended
Dec. 31, 2016
USD ($)
$ / participant
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Jan. 01, 2017
USD ($)
Accounting Policies [Abstract]        
Maximum exposure, per participant | $ / participant 100,000      
Restricted cash, noncurrent $ 19,920,000 $ 13,515,000    
Interest costs capitalized 1,253,000 941,000 $ 518,000  
Proceeds from Section 1603 grants 0 0 $ 3,727,000  
Deferred grant income 7,739,000 8,291,000    
Carrying value of fixed-rate long-term debt in excess of fair value 508,000      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Credit to retained earnings $ (194,353,000) $ (182,321,000)    
Subsequent Event | New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2016-09        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Deferred income tax assets, net       $ 4,000,000
Credit to retained earnings       $ 4,000,000