Preferred Stock (Schedule of Preferred Stock ) (Detail) - USD ($) $ / shares in Units, $ in Thousands | 9 Months Ended | | |
Sep. 30, 2018 | Jan. 03, 2018 | Dec. 31, 2017 |
Class of Stock [Line Items] | | | |
Preferred stock | $ 368,767 | | $ 263,317 |
Series B Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred stock | $ 187,190 | | 146,649 |
Preferred shares issued at $0.01 par value (in shares) | 155,000 | | |
Preferred stock, par value (in dollars per share) | $ 0.01 | | |
Preferred Stock, Shares Outstanding | 155,000 | | |
Share issued, price per share (in dollars per share) | $ 1,000 | | |
Preferred Stock, Dividend Rate, Percentage | 17.573% | | |
Preferred stock redemption term | 8 years | | |
Series B Preferred Stock | 12 - 24 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 105.00% | | |
Series B Preferred Stock | 24 - 36 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 103.00% | | |
Series B Preferred Stock | Minimum | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component two | 4.75% | | |
Series B Preferred Stock | Maximum | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component two | 12.50% | | |
Series B Preferred Stock | London Interbank Offered Rate (LIBOR) | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component one, basis spread on variable rate | 3.00% | | |
Series C Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred stock | $ 94,358 | | 76,096 |
Preferred shares issued at $0.01 par value (in shares) | 55,000 | | |
Preferred Stock, Shares Outstanding | 55,000 | | |
Share issued, price per share (in dollars per share) | $ 1,000 | | |
Preferred Stock, Dividend Rate, Percentage | 17.573% | | |
Preferred stock redemption term | 8 years | | |
Series C Preferred Stock | 0 - 12 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 65.00% | | |
Series C Preferred Stock | Minimum | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component two | 4.75% | | |
Series C Preferred Stock | Maximum | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component two | 12.50% | | |
Series C Preferred Stock | London Interbank Offered Rate (LIBOR) | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component one, basis spread on variable rate | 3.00% | | |
Series D Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred stock | $ 1,159 | | 6,672 |
Preferred shares issued at $0.01 par value (in shares) | 100 | | |
Preferred Stock, Shares Outstanding | 100 | | |
Share issued, price per share (in dollars per share) | $ 1 | | |
Preferred stock redemption term | 8 years | | |
Series E Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred stock | $ 43,387 | | 33,900 |
Preferred shares issued at $0.01 par value (in shares) | 90,000 | | |
Preferred Stock, Shares Outstanding | 37,500 | | |
Share issued, price per share (in dollars per share) | $ 1,000 | | |
Dividend rate, component two | 8.50% | | |
Preferred Stock, Dividend Rate, Percentage | 15.823% | | |
Preferred stock redemption term | 6 years | | |
Series E Preferred Stock | 12 - 24 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 103.50% | | |
Series E Preferred Stock | 0 - 12 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 106.50% | | |
Series E Preferred Stock | London Interbank Offered Rate (LIBOR) | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component one, basis spread on variable rate | 5.25% | | |
Series F Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred shares issued at $0.01 par value (in shares) | 35,728 | | |
Preferred Stock, Shares Outstanding | 35,728 | | |
Share issued, price per share (in dollars per share) | $ 1,000 | | |
Preferred Stock, Dividend Rate, Percentage | 15.823% | | |
Preferred stock redemption term | 6 years | | |
Series F Preferred Stock | 12 - 24 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 103.50% | | |
Series F Preferred Stock | 0 - 12 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 106.50% | | |
Series F Preferred Stock | Refinancing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 101.00% | | |
Series F Preferred Stock | London Interbank Offered Rate (LIBOR) | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component one, basis spread on variable rate | 5.25% | | |
Series E-1 Preferred Stock | | | |
Class of Stock [Line Items] | | | |
Preferred stock | $ 42,673 | | $ 0 |
Preferred stock, par value (in dollars per share) | | $ 0.01 | |
Share issued, price per share (in dollars per share) | $ 1,000 | | |
Series E-1 Preferred Stock | 12 - 24 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 103.50% | | |
Series E-1 Preferred Stock | 0 - 12 months from closing date | | | |
Class of Stock [Line Items] | | | |
Preferred stock redemption rights | 106.50% | | |
Series E-1 Preferred Stock | London Interbank Offered Rate (LIBOR) | | | |
Class of Stock [Line Items] | | | |
Dividend rate, component one, basis spread on variable rate | 5.25% | | |
Series E-1 Preferred Stock, Option 2 | | | |
Class of Stock [Line Items] | | | |
Share issued, price per share (in dollars per share) | $ 960 | | |