Redeemable Preferred Stocks Exchanged for Common Stock - Summary of Redeemable Preferred Stocks Exchanged for Common Stock (Detail) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders Equity [Line Items]
Beginning balance			$ 1,029,000				$ 1,029,000
Accumulated dividends	$ 10,190,000	$ 10,213,000	9,511,000	$ 8,889,000	$ 8,689,000	$ 8,307,000
Series E Redeemable Preferred Stock [Member]
Stockholders Equity [Line Items]
Beginning balance			$ 272,101,000				$ 272,101,000
Beginning balance, shares			139,768				139,768
Accretion relating to liquidation preference on preferred stock							$ 814,000
Accretion for discount and issuance costs on preferred stock							709,000
Accumulated dividends	$ 10,190,000			$ 8,889,000			29,914,000	$ 25,885,000
Costs relating to exchange transaction							(7,497,000)
Exchange of preferred stock for common stock							$ (296,041,000)
Exchange of preferred stock for common stock, shares							(139,768)
Series E Redeemable Preferred Stock [Member] | Accrued Liability Embedded Derivative [Member]
Stockholders Equity [Line Items]
Beginning balance			$ 1,029,000				$ 1,029,000
Change in fair value of embedded derivative							2,258,000
Exchange of preferred stock for common stock							$ (3,287,000)
Series F Redeemable Preferred Stock [Member]
Stockholders Equity [Line Items]
Beginning balance, shares			1				1
Exchange of preferred stock for common stock, shares							(1)