Fair Value Measurements - Schedule of Change in Valuation of Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Equity securities and warrants beginning balance	$ 2,768	$ 2,768	$ 2,768
Purchase of additional common stock	500	0	0
Investment impairment charges	(4,678)
Equity securities and warrants ending balance	219	2,768	2,768
ASU 2016-01 [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Impact of adoption of ASU 2016-01 recognized in other income	$ 1,629	$ 0	$ 0