Share-based Compensation - Stock Appreciation Rights (Details) - Stock Appreciation Rights (SARs) [Member] - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		5 years
Additional expense from accelerated vesting	$ 3.2
Outstanding at beginning of period (in shares)		65,250	72,500
Exercised (in shares)		(63,250)	(2,175)
Canceled or expired (in shares)		(2,000)	(5,075)
Outstanding at end of period (in shares)			65,250
Grant date exercise price, outstanding awards at beginning of period		$ 9.95	$ 9.95
Grant date exercise price, exercised		9.95	9.95
Grant date exercise price, canceled or forfeited		$ 9.95	9.95
Grant date exercise price, outstanding awards at end of period			$ 9.95
Share-based compensation recognized cost		$ 3.4	$ 0.3