Series D Preferred Shares - Additional Information (Detail)	Jun. 27, 2018 USD ($) shares	Mar. 19, 2018 USD ($) shares	Jun. 22, 2017 USD ($) shares	Dec. 07, 2016 USD ($) shares	Mar. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares	Dec. 31, 2017 shares	Oct. 18, 2017 USD ($)	Oct. 17, 2017 USD ($)	Oct. 11, 2017 USD ($)	Dec. 31, 2015 shares	Sep. 30, 2015 USD ($) Covenant	Oct. 01, 2012 USD ($) $ / shares shares
Temporary Equity [Line Items]
Stock Appreciation Rights													6,735,667
Redemption and Exchange Agreement
Temporary Equity [Line Items]
Share repurchase, exchange fees | $	$ 418,000
Adjusted
Temporary Equity [Line Items]
Warrants exercisable for common shares					11,035,875
Stock Appreciation Rights					7,485,045
ARS VI
Temporary Equity [Line Items]
Aggregate purchase price under Securities Purchase Agreement | $													$ 100,000,000
ARS VI | Warrants and investor SARs
Temporary Equity [Line Items]
Class of warrant and right exercise of purchase value. | $										$ 20,500,000
Fair value adjustment of warrants and investor rights obligation | $								$ 0
Warrants and rights outstanding | $									$ 0
Preferred Series D
Temporary Equity [Line Items]
Cumulative redeemable preferred shares, shares issued		2,939,190	3,133,720	3,536,000			3,133,720				4,000,000
Preferred shares with warrants													9,931,000
Shares repurchase and cancel, shares		194,530	402,280	464,000
Repurchase shares price | $		$ 4,863,000	$ 10,057,000	$ 11,600,000
Cumulative redeemable preferred shares, shares outstanding		2,939,190	3,133,720	3,536,000			3,133,720				4,000,000
Preferred Series D | Redemption and Exchange Agreement
Temporary Equity [Line Items]
Repurchase shares price | $	$ 56,765,000
Shares repurchased and cancelled, shares	2,939,190
Preferred Series D | ARS VI
Temporary Equity [Line Items]
Cumulative redeemable preferred shares, shares issued													4,000,000
Cumulative Redeemable Preferred Shares, par value | $ / shares													$ 0.01
Number of covenants | Covenant												2
Consideration paid under Securities Purchase Agreement | $												$ 450,000
Preferred Series A, B, and C | Redemption and Exchange Agreement
Temporary Equity [Line Items]
Liquidation preference | $	$ 16,715,000
7.75% Series A Cumulative Redeemable Preferred Stock
Temporary Equity [Line Items]
Cumulative Redeemable Preferred Shares, par value | $ / shares					$ 0.01	$ 0.01
7.75% Series A Cumulative Redeemable Preferred Stock | Redemption and Exchange Agreement
Temporary Equity [Line Items]
Preferred shares issued, net (shares)	383,147
8.375% Series B Cumulative Redeemable Preferred Stock
Temporary Equity [Line Items]
Cumulative Redeemable Preferred Shares, par value | $ / shares					0.01	0.01
8.375% Series B Cumulative Redeemable Preferred Stock | Redemption and Exchange Agreement
Temporary Equity [Line Items]
Preferred shares issued, net (shares)	167,828
8.875% Series C Cumulative Redeemable Preferred Stock
Temporary Equity [Line Items]
Cumulative Redeemable Preferred Shares, par value | $ / shares					$ 0.01	$ 0.01
8.875% Series C Cumulative Redeemable Preferred Stock | Redemption and Exchange Agreement
Temporary Equity [Line Items]
Preferred shares issued, net (shares)	117,605