Convertible Notes (Summary of Convertible Notes) (Detail)			3 Months Ended	9 Months Ended
	Nov. 21, 2016	Feb. 11, 2014	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 22, 2016 $ / shares	Feb. 12, 2014 $ / shares
Debt Instrument [Line Items]
Principal amount a $5 incentive cash payment per each to convert debt			$ 1,000	$ 1,000
Convertible Notes Payable, Carrying Value			240,638,000	$ 240,638,000	$ 232,443,000
February 2018 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage							4.00%
Debt Instrument, Convertible, Conversion Ratio		109.1048
Convertible notes, conversion price (in Dollars per Share) | $ / shares							$ 9.17
Convertible Notes, Maturity Date (Date)				Feb. 01, 2018
Convertible Notes, Principal Balance Outstanding			126,447,000	$ 126,447,000	126,447,000
Convertible Notes Payable, Carrying Value			124,922,000	$ 124,922,000	121,595,000
December 2021 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						2.80%
Debt Instrument, Convertible, Conversion Ratio	262.2951
Convertible notes, conversion price (in Dollars per Share) | $ / shares						$ 3.81
Convertible Notes, Maturity Date (Date)				Dec. 01, 2021
Convertible Notes, Principal Balance Outstanding			150,000,000	$ 150,000,000	150,000,000
Convertible Notes Payable, Carrying Value			$ 115,716,000	$ 115,716,000	$ 110,848,000