Financing Arrangements - underwritten public offering (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Financing Arrangements
Underwritten public offering (in shares)	3,300,000
Period to exercise additional shares	30 years
Additional shares granted to underwriters to purchase additional shares	495,000
Shares exercised by underwriters	495,000
Offered price (per share) | $ / shares	$ 60.00
Net Proceeds from public offering | $	$ 215.8
Underwriting discounts and commissions and offering expenses | $	$ 11.9