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Distributions - Summary of Distributions Paid Including Activity in Plan as well as Limited Partnership Units Issued from Reinvestment of Unit Distributions (Detail) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
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Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Dividends [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stockholders |  |  |  |  |  |  |  |  |  |  |  |  | $ 11,194 | $ 12,390 | $ 12,402
Common Stockholders |  |  |  |  |  |  |  |  |  |  |  |  | 49,383 | 48,568 | 46,306
Limited Partnership Unitholders |  |  |  |  |  |  |  |  |  |  |  |  | $ 16,751 | $ 16,642 | $ 15,981
Common Stock Shares Issued (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 228,498,000 | 430,462,000 | 572,928,000
Limited Partnership Units Issued (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 51,579,000 | 60,936,000 | 107,433,000
4th Quarter |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stockholders | $ 2,798 |  |  |  | $ 3,531 |  |  |  | $ 2,953 |  |  |  |  |  |
Common Stockholders | 12,371 |  |  |  | 12,251 |  |  |  | 11,706 |  |  |  |  |  |
Limited Partnership Unitholders | $ 4,195 |  |  |  | $ 4,173 |  |  |  | $ 4,062 |  |  |  |  |  |
Common Stock Shares Issued (in shares) | 117,368,000 |  |  |  | 104,558,000 |  |  |  | 216,476,000 |  |  |  |  |  |
Discounted Share Price (in usd per share) | $ 24.08 |  |  |  | $ 52.84 |  |  |  | $ 49.34 |  |  |  | $ 24.08 | $ 52.84 | $ 49.34
Limited Partnership Units Issued (in shares) | 23,370,000 |  |  |  | 13,747,000 |  |  |  | 13,867,000 |  |  |  |  |  |
Average Unit Price (in usd per share) | $ 24.35 |  |  |  | $ 53.73 |  |  |  | $ 50.20 |  |  |  | $ 24.35 | $ 53.73 | $ 50.20
3rd Quarter |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stockholders |  | $ 2,798 |  |  |  | $ 2,953 |  |  |  | $ 2,953 |  |  |  |  |
Common Stockholders |  | 12,373 |  |  |  | 12,195 |  |  |  | 11,590 |  |  |  |  |
Limited Partnership Unitholders |  | $ 4,188 |  |  |  | $ 4,166 |  |  |  | $ 4,055 |  |  |  |  |
Common Stock Shares Issued (in shares) |  | 14,525,000 |  |  |  | 105,753,000 |  |  |  | 201,500,000 |  |  |  |  |
Discounted Share Price (in usd per share) |  | $ 28.98 |  |  |  | $ 53.66 |  |  |  | $ 51.68 |  |  |  |  |
Limited Partnership Units Issued (in shares) |  | 13,108,000 |  |  |  | 13,406,000 |  |  |  | 13,107,000 |  |  |  |  |
Average Unit Price (in usd per share) |  | $ 29.47 |  |  |  | $ 54.56 |  |  |  | $ 52.60 |  |  |  |  |
2nd Quarter |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stockholders |  |  | $ 2,799 |  |  |  | $ 2,953 |  |  |  | $ 2,672 |  |  |  |
Common Stockholders |  |  | 12,364 |  |  |  | 12,116 |  |  |  | 11,545 |  |  |  |
Limited Partnership Unitholders |  |  | $ 4,188 |  |  |  | $ 4,155 |  |  |  | $ 3,942 |  |  |  |
Common Stock Shares Issued (in shares) |  |  | 12,627,000 |  |  |  | 99,804,000 |  |  |  | 85,202,000 |  |  |  |
Discounted Share Price (in usd per share) |  |  | $ 32.22 |  |  |  | $ 51.38 |  |  |  | $ 47.54 |  |  |  |
Limited Partnership Units Issued (in shares) |  |  | 0 |  |  |  | 20,041,000 |  |  |  | 42,422,000 |  |  |  |
Average Unit Price (in usd per share) |  |  | $ 0 |  |  |  | $ 51.99 |  |  |  | $ 47.83 |  |  |  |
1st Quarter |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stockholders |  |  |  | $ 2,799 |  |  |  | $ 2,953 |  |  |  | $ 3,824 |  |  |
Common Stockholders |  |  |  | 12,275 |  |  |  | 12,006 |  |  |  | 11,465 |  |  |
Limited Partnership Unitholders |  |  |  | $ 4,180 |  |  |  | $ 4,148 |  |  |  | $ 3,922 |  |  |
Common Stock Shares Issued (in shares) |  |  |  | 83,978,000 |  |  |  | 120,347,000 |  |  |  | 69,750,000 |  |  |
Discounted Share Price (in usd per share) |  |  |  | $ 48.59 |  |  |  | $ 51.28 |  |  |  | $ 52.71 |  |  |
Limited Partnership Units Issued (in shares) |  |  |  | 15,101,000 |  |  |  | 13,742,000 |  |  |  | 38,037,000 |  |  |
Average Unit Price (in usd per share) |  |  |  | $ 49.40 |  |  |  | $ 52.16 |  |  |  | $ 53.03 |  |  |

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