Financial Assets and Liabilities Accounted For at Fair Value on Recurring Basis (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	$ 331,806	$ 370,595
Convertible senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	133,582	130,628
Term loan credit agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	188,832	229,388
Industrial revenue bond
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	1,765	2,119
Capital lease obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	7,627	8,460
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 1 | Convertible senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 1 | Term loan credit agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 1 | Industrial revenue bond
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 1 | Capital lease obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	389,759	434,402
Fair Value, Inputs, Level 2 | Convertible senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	198,360	197,718
Fair Value, Inputs, Level 2 | Term loan credit agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	191,399	236,684
Fair Value, Inputs, Level 2 | Industrial revenue bond
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 2 | Capital lease obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	9,392	10,579
Fair Value, Inputs, Level 3 | Convertible senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 3 | Term loan credit agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	0	0
Fair Value, Inputs, Level 3 | Industrial revenue bond
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	1,765	2,119
Fair Value, Inputs, Level 3 | Capital lease obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure, recurring	$ 7,627	$ 8,460