Dividends Declared and Paid on Preferred Shares (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2016	Jun. 30, 2016
Dividends [Line Items]
Total dividend amount		$ 13,669
Preferred Stock | 7.75% Series A Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared	Feb. 16, 2016	May 19, 2016
Record date	Mar. 01, 2016	Jun. 01, 2016
Date paid	Mar. 31, 2016	Jun. 30, 2016
Total dividend amount	$ 2,570	$ 2,570
Preferred Stock | 8.375% Series B Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared	Feb. 16, 2016	May 19, 2016
Record date	Mar. 01, 2016	Jun. 01, 2016
Date paid	Mar. 31, 2016	Jun. 30, 2016
Total dividend amount	$ 1,225	$ 1,225
Preferred Stock | 8.875% Series C Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Date declared	Feb. 16, 2016	May 19, 2016
Record date	Mar. 01, 2016	Jun. 01, 2016
Date paid	Mar. 31, 2016	Jun. 30, 2016
Total dividend amount	$ 910	$ 910
Preferred Stock | Series D cumulative redeemable preferred shares
Dividends [Line Items]
Date declared	Feb. 16, 2016	May 19, 2016
Record date	Mar. 01, 2016	Jun. 01, 2016
Date paid	Mar. 31, 2016	Jun. 30, 2016
Total dividend amount	$ 2,125	$ 2,125