Equity - Restricted Stock (Details) - Restricted stock and performance-based stock units - USD ($)	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Restricted stock awards
Number of shares granted	167,375	147,608
Compensation expense related to share-based award	$ 3,539,000	$ 3,312,000
Nonvested awards
Remaining compensation expense	11,772,000
2020
Nonvested awards
Remaining compensation expense	3,566,000
2021
Nonvested awards
Remaining compensation expense	5,201,000
2022
Nonvested awards
Remaining compensation expense	2,729,000
2023
Nonvested awards
Remaining compensation expense	$ 276,000
Grant Date Price $48.95 \| Three year vesting
Restricted stock awards
Number of shares granted	76,464
Granted (in dollars per share)	$ 48.95
Vesting period	3 years
Grant Date Price $49.98 \| TSR Targets
Restricted stock awards
Number of shares granted	66,027
Granted (in dollars per share)	$ 49.98
Vesting period	4 years
Grant Date Price $49.98 \| Accelerated TSR Targets
Restricted stock awards
Vesting period	3 years
Grant Date Price $38.45 \| Three year vesting
Restricted stock awards
Number of shares granted	15,000
Granted (in dollars per share)	$ 38.45
Vesting period	3 years
Grant Date Price $38.45 \| Vesting Date, May 27, 2021
Restricted stock awards
Number of shares granted	9,884
Granted (in dollars per share)	$ 38.45
Grant Date Price $46.54 \| Three year vesting
Restricted stock awards
Number of shares granted		78,276
Granted (in dollars per share)		$ 46.54
Vesting period		3 years
Grant Date Price $46.54 \| TSR Targets
Restricted stock awards
Number of shares granted		60,836
Granted (in dollars per share)		$ 46.54
Vesting period		4 years
Grant Date Price $46.54 \| Accelerated TSR Targets
Restricted stock awards
Vesting period		3 years
Grant Date Price $44.73 \| Vesting Date, May 29, 2020
Restricted stock awards
Number of shares granted		8,496
Granted (in dollars per share)		$ 44.73

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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-Name Accounting Standards Codification
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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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