Stock-based Compensation (Details) - Equity Incentive Plan - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based Compensation
Recorded compensation costs for the RSAs and RSUs	$ 1.2	$ 0.8	$ 3.9	$ 1.5
Restricted Stock Awards (RSAs)
Stock-based Compensation
Weighted average grant date fair value (in dollars per share)			$ 52.83	$ 35.40
Restricted Stock Awards (RSAs) \| Officers and Directors
Stock-based Compensation
Awards granted (in shares)	0	0	36,183	46,135
Awards canceled (in shares)	2,544	3,842	10,878	13,306
Restricted Stock Awards (RSAs) \| Director
Stock-based Compensation
Vesting period			12 months
Restricted Stock Awards (RSAs) \| Officer
Stock-based Compensation
Vesting period			36 months
Restricted Stock Unit Award (RSUs) \| Officer
Stock-based Compensation
Awards granted (in shares)	0	0	26,473	28,594
Awards canceled (in shares)	0	0	31,177	24,009
Weighted average grant date fair value (in dollars per share)			$ 52.83	$ 35.40
Awards issued (in shares)	0	0	62,726	48,753
Expiration period of award			3 years

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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