Dividends Declared and Paid on Preferred Shares (Detail) - USD ($) $ in Thousands				3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 23, 2017	Jun. 22, 2017	Mar. 31, 2017	Jun. 30, 2017
Dividends [Line Items]
Total dividend amount					$ 13,213
Series D cumulative redeemable preferred shares
Dividends [Line Items]
Date declared			May 18, 2017
Record date			Jun. 01, 2017
Date paid	Jun. 30, 2017	Jun. 23, 2017
Total dividend amount			$ 1,879
Preferred Stock | 7.75% Series A Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared				Feb. 15, 2017	May 18, 2017
Record date				Mar. 01, 2017	Jun. 01, 2017
Date paid				Mar. 31, 2017	Jun. 30, 2017
Total dividend amount				$ 2,589	$ 2,589
Preferred Stock | 8.375% Series B Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared				Feb. 15, 2017	May 18, 2017
Record date				Mar. 01, 2017	Jun. 01, 2017
Date paid				Mar. 31, 2017	Jun. 30, 2017
Total dividend amount				$ 1,225	$ 1,225
Preferred Stock | 8.875% Series C Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared				Feb. 15, 2017	May 18, 2017
Record date				Mar. 01, 2017	Jun. 01, 2017
Date paid				Mar. 31, 2017	Jun. 30, 2017
Total dividend amount				$ 910	$ 910
Preferred Stock | Series D cumulative redeemable preferred shares
Dividends [Line Items]
Date declared				Feb. 15, 2017	May 18, 2017
Record date				Mar. 01, 2017	Jun. 01, 2017
Date paid				Mar. 31, 2017	Jun. 30, 2017
Total dividend amount				$ 1,879	$ 1,879