Convertible Notes (Summary of Convertible Notes) (Detail) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended			4 Months Ended	5 Months Ended	8 Months Ended	12 Months Ended
	Nov. 20, 2015 USD ($)	Sep. 30, 2020	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Aug. 18, 2020	Sep. 30, 2020	May 20, 2020 USD ($)	Aug. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 01, 2020 $ / shares	May 21, 2020 $ / shares	Sep. 17, 2019 $ / shares	Nov. 22, 2016 $ / shares	Feb. 12, 2014
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months			$ 405
Repayments of Notes Payable								$ 0	$ 0	$ (126,447)
Convertible Notes and Term Loans, Beginning Balance							$ 27,250	27,250
Gains (Losses) on Extinguishment of Debt				$ 3,900				606	8,430	0
Convertible Notes and Term Loans, Ending Balance									27,250
Long-term Debt, Maturities, Repayments of Principal in Year Two			0
Long-term Debt, Maturities, Repayments of Principal in Year Three			0
Long-term Debt, Maturities, Repayments of Principal in Year Four			0
Long-term Debt, Maturities, Repayments of Principal in Year Five			0
Long-term Debt, Maturities, Repayments of Principal after Year Five			0
Long-term Debt			405
December 2024 Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months			$ 0
Debt Instrument, Interest Rate, Stated Percentage													2.75%
Debt Instrument, Convertible, Conversion Ratio		378.8004	410.6268			316.5801	262.2951
Convertible notes, conversion price (in Dollars per Share) | $ / shares											$ 2.44	$ 3.16	$ 3.81
Convertible Notes, Principal Balance Outstanding									11,500
Convertible Notes and Term Loans, Beginning Balance							$ 10,300	10,300
Gains (Losses) on Extinguishment of Debt									(2,100)
Convertible Notes and Term Loans, Ending Balance									10,300
Long-term Debt, Maturities, Repayments of Principal in Year Two			$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Three			0
Long-term Debt, Maturities, Repayments of Principal in Year Four			0
Long-term Debt, Maturities, Repayments of Principal in Year Five			0
Long-term Debt, Maturities, Repayments of Principal after Year Five			0
Long-term Debt			0
February 2018 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage															4.00%
Gains (Losses) on Extinguishment of Debt	$ (6,500)
Amortization of Debt Discount (Premium)										293
December 2021 Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months			$ 405
Debt Instrument, Interest Rate, Stated Percentage														2.75%
Debt Instrument, Convertible, Conversion Ratio		343.1098	410.6268		316.5801		262.2951
Convertible notes, conversion price (in Dollars per Share) | $ / shares											$ 2.44	$ 3.16		$ 3.81
Convertible Notes, Principal Balance Outstanding			$ 2,330						19,170
Convertible Notes and Term Loans, Beginning Balance							$ 16,950	16,950
Gains (Losses) on Extinguishment of Debt									(2,500)
Amortization of Debt Discount (Premium)								$ 39	459	$ 542
Convertible Notes and Term Loans, Ending Balance									$ 16,950
Long-term Debt, Maturities, Repayments of Principal in Year Two			0
Long-term Debt, Maturities, Repayments of Principal in Year Three			0
Long-term Debt, Maturities, Repayments of Principal in Year Four			0
Long-term Debt, Maturities, Repayments of Principal in Year Five			0
Long-term Debt, Maturities, Repayments of Principal after Year Five			0
Long-term Debt			$ 405