Summary of Series B Preferred Stock and Accretion of Dividends (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Stockholders Equity [Line Items]
Cumulative dividends on Series B preferred stock	$ 259	$ 517
Series B Preferred Stock
Stockholders Equity [Line Items]
Balance at December 31, 2018		20,833
Cumulative dividends on Series B preferred stock		517
Balance at June 30, 2019	$ 21,350	$ 21,350
Balance at December 31, 2018, Shares		5,208
Cumulative dividends on Series B preferred stock, Shares		130
Balance at March 31, 2019, Shares	5,338	5,338
Series B Preferred Stock | Tranche One
Stockholders Equity [Line Items]
Balance at December 31, 2018		$ 12,600
Cumulative dividends on Series B preferred stock		315
Balance at June 30, 2019	$ 12,915	$ 12,915
Balance at December 31, 2018, Shares		3,150
Cumulative dividends on Series B preferred stock, Shares		79
Balance at March 31, 2019, Shares	3,229	3,229
Series B Preferred Stock | Tranche Two
Stockholders Equity [Line Items]
Balance at December 31, 2018		$ 8,233
Cumulative dividends on Series B preferred stock		202
Balance at June 30, 2019	$ 8,435	$ 8,435
Balance at December 31, 2018, Shares		2,058
Cumulative dividends on Series B preferred stock, Shares		51
Balance at March 31, 2019, Shares	2,109	2,109