Common Stock Incentive Plan - Restricted Stock (Details) - Restricted Stock $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) shares
Common Stock Incentive Plan
Shares granted in period (in shares)	79,927
Unamortized share-based compensation expense | $	$ 13.0
Board of Directors
Common Stock Incentive Plan
Shares granted in period (in shares)	32,000
Board of Directors | Vest immediately
Common Stock Incentive Plan
Shares granted in period (in shares)	20,000
Board of Directors | Vest over one-year service period
Common Stock Incentive Plan
Shares granted in period (in shares)	4,000
Vesting period (in years)	1 year
Board of Directors | Vest over three-year service period
Common Stock Incentive Plan
Shares granted in period (in shares)	8,000
Vesting period (in years)	3 years
Employees | Vest over four-year service period
Common Stock Incentive Plan
Vesting period (in years)	4 years