Dividends/Distributions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Dividends [Line Items]
Dividends declared	$ 90,177	$ 81,408		$ 243,928	$ 81,534
Dividends declared, per share	$ 0.91	$ 0.83	$ 2.73	$ 2.49	$ 0.83
Distributions paid, preferred stockholders	$ 91	$ 91	$ 364	$ 273
Distributions paid, preferred stockholders, per share	$ 15.95	$ 15.95	$ 63.80	$ 47.85
Taxable Income Distribution [Member]
Dividends [Line Items]
Distributions paid			$ 351,036
Distributions paid, per share			$ 3.56

Dividends [Line Items]

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- Definition

Amount paid and unpaid per share for dividends of preferred stock.

+ References

No definition available.

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- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Aggregate dividends declared during the period for each share of common stock outstanding.

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Amount of paid and unpaid cash dividends declared for classes of stock, for example, but not limited to, common and preferred.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 45
-Paragraph 2
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- Definition

Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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-Publisher FASB
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