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Stock Option Plans - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Sep. 30, 2019	Mar. 31, 2020	Mar. 31, 2018	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation (in shares)	109,762	2,191
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)		0	485
Stock option expense		$ 0.4
Future expense		$ 2.3
Closing share price (in usd per share)		$ 32.74
Granted (in shares)		1,298,865		1,309,614
Weighted average remaining contractual life of the Company's outstanding options		6 years 8 months 12 days
Weighted average remaining contractual life of the Company's exercisable options		5 years 8 months 12 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)		6,837
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Officers \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
2010-2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)		1,298,865