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Schedule of Amortization of Premium and Accretion of Debt Issuance Costs (Detail) - 5.75% Senior convertible notes due August 15, 2018 - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Debt Instrument [Line Items]        
Amortization of debt premium $ 61 $ 58 $ 120 $ 115
Accretion expense-debt issuance cost $ 68 $ 63 $ 134 $ 126