Credit Agreement (Details)		1 Months Ended	9 Months Ended
	Dec. 19, 2017 USD ($)	May 31, 2013 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount			$ 6,500,000
Amortization of interest expense			423,000	$ 423,000
Credit Agreement
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 500,000,000	$ 500,000,000
Line of credit facility, expiration period	5 years	5 years
Debt agreement, maximum borrowing capacity	$ 120,000,000
Debt agreement, maximum borrowing capacity percent of consolidated EBITDA	100.00%
Credit Agreement | Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 50,000,000
Line of credit facility, unused capacity, commitment fee percentage	0.125%
Credit Agreement | Swingline Loans
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25,000,000
Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, covenant, interest coverage ratio	5.25
Long-term line of credit, total			240,000,000		$ 240,000,000
Repayments of long-term lines of credit			0
Debt issuance costs, net			1,300,000		$ 1,700,000
Amortization of interest expense			$ 400,000	$ 400,000
Credit Agreement | Revolving Credit Facility | Fed Funds Effective Rate Overnight Index Swap Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	0.50%
Credit Agreement | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	1.00%
Credit Agreement | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.375%
Debt instrument, secured leverage ratio	3
Credit Agreement | Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	0.50%
Credit Agreement | Revolving Credit Facility | Minimum | One-month LIBOR Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	1.50%
Credit Agreement | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Debt instrument, covenant, interest coverage ratio	3.00
Line of credit facility, unused capacity, commitment fee percentage	0.25%
Credit Agreement | Revolving Credit Facility | Maximum | From and After January 2020
Line of Credit Facility [Line Items]
Debt instrument, covenant, interest coverage ratio	4.25
Credit Agreement | Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	1.00%
Credit Agreement | Revolving Credit Facility | Maximum | One-month LIBOR Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.00%