Income Taxes - Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Net operating losses	$ 61,189	$ 54,407
Capitalized research and development expenses	564	705
Credit carryforwards	166,459	166,367
Depreciation		2,725
Deferred compensation	1,479	6,315
Election out of installment method	820
Accrued expenses		655
Other temporary differences	1,089	2,423
Installment sale tax basis	15,868	14,881
Total gross deferred tax assets	247,468	248,478
Valuation allowance	$ (247,468)	$ (248,478)	$ (236,067)