Fair Value Measurement (Narrative) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) Agreement	Dec. 31, 2018 USD ($)
Credit Derivatives [Line Items]
Fair value of funded deferred compensation assets	$ 25,200,000	$ 24,100,000
Separate line of credit agreements (in agreements) | Agreement	2
Fair Value, Measurements, Nonrecurring
Credit Derivatives [Line Items]
Fair value, net asset (liability)	$ 0	$ 0
Corporate debt, limited observable inputs | NRSRO, Rating BBB Plus
Credit Derivatives [Line Items]
Credit rating	57.00%	54.00%
Other asset-backed securities | NRSRO, Rating AA Minus
Credit Derivatives [Line Items]
Credit rating	42.00%
Other asset-backed securities | NRSRO, Rating AAA
Credit Derivatives [Line Items]
Credit rating		25.00%