Equity Compensation Plans - Unrecognized Compensation Cost (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	$ 25,122
Equity grants	8,474
Equity grant forfeitures	0
Equity compensation expense	(10,132)
Unrecognized Compensation Cost at End of Period	23,464
Incentive Plans | Restricted Stock Awards
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	3,498
Equity grants	0
Equity grant forfeitures	0
Equity compensation expense	(1,137)
Unrecognized Compensation Cost at End of Period	2,361
Incentive Plans | Restricted Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	74
Equity grants	3,483
Equity grant forfeitures	0
Equity compensation expense	(499)
Unrecognized Compensation Cost at End of Period	3,058
Incentive Plans | Deferred Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	14,489
Equity grants	4,831
Equity grant forfeitures	0
Equity compensation expense	(5,871)
Unrecognized Compensation Cost at End of Period	13,449
Incentive Plans | Performance Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	7,061
Equity grants	0
Equity grant forfeitures	0
Equity compensation expense	(2,505)
Unrecognized Compensation Cost at End of Period	4,556
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	0
Equity grants	160
Equity grant forfeitures	0
Equity compensation expense	(120)
Unrecognized Compensation Cost at End of Period	$ 40