Common Stock Incentive Plan - Performance Shares and Restricted Stock Units (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) shares
Performance Shares and Restricted Stock Units
Common Stock Incentive Plan
Unamortized share-based compensation expense \| $	$ 13.8
Performance Shares
Common Stock Incentive Plan
Shares granted in period (in shares)	115,137
Vesting rights percentage	50.00%
Vesting period (in years)	3 years
Restricted Stock Units
Common Stock Incentive Plan
Shares granted in period (in shares)	5,482
Vesting period (in years)	4 years

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 718
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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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).

+ References

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Percentage of vesting of share-based compensation awards.

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