Common Stock Incentive Plan - Performance Shares (Details) - Performance Shares - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock Incentive Plan
Vesting rights percentage	50.00%
Performance period (in years)	3 years
Remaining unamortized share-based compensation expense	$ 8.7
Performance shares vesting based on achievement of performance goals
Total shareholder return (TSR) relative to MSCI US REIT Index (as a percent)	45.00%	45.00%	45.00%
TSR relative to JP Morgan Net Lease Peers (as a percent)	26.00%	26.00%	26.00%
Dividend per share growth rate (as a percent)	16.00%	16.00%	16.00%
Debt-to-EBITDA ratio (as a percent)	13.00%	13.00%	13.00%
Number of shares
Outstanding nonvested shares, beginning of year	223,392	245,309	159,751
Shares granted	128,581	269,868	124,681
Shares vested	(47,310)	(291,785)	(39,123)
Shares forfeited	0	0	0
Outstanding nonvested shares, end of each period	304,663	223,392	245,309
Weighted average price
Outstanding nonvested shares, beginning of year (in dollars per share)	$ 58.78	$ 62.49	$ 49.95
Shares granted (in dollars per share)	65.34	51.98	71.79
Shares vested (in dollars per share)	54.27	54.88	41.60
Shares forfeited (in dollars per share)	0	0	0
Outstanding nonvested shares, end of each period (in dollars per share)	$ 62.25	$ 58.78	$ 62.49

Number of performance shares that vest based on the achievement of performance goals.

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Represents the percentage of share-based compensation award value relative to the Debt-to-EBITDA ratio.

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Represents the percentage of share-based compensation award value relative to the dividend growth rate.

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Represents the percentage of share-based compensation award value relative to the PP Morgan Net Lease Peers.

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- Definition

Represents the percentage of share-based compensation TSR value relative to the RMS Index.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage of vesting of award under share-based payment arrangement.

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