Line of Credit (Details) - USD ($)		9 Months Ended
	Jun. 13, 2016	Sep. 30, 2019
Line of Credit Facility [Line Items]
Letters of credit outstanding amount		$ 11,553,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility term of agreement	5 years
Credit facility maximum borrowing capacity	$ 300,000,000
Credit facility stated percentage	0.00%
Credit facility accordion feature, increase limit	$ 100,000,000
Credit facility remaining borrowing capacity		288,447,000
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	1.00%
Revolving Credit Facility | Federal Funds Rate
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	0.50%
Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Credit facility commitment fee per annum on daily unused portion	0.15%
Revolving Credit Facility | Minimum | Lender's Base Rate Plus Market Spread
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	0.25%
Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	1.25%
Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Credit facility commitment fee per annum on daily unused portion	0.30%
Revolving Credit Facility | Maximum | Lender's Base Rate Plus Market Spread
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	1.00%
Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Credit facility variable interest rate basis spread	2.00%
Letter of Credit
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity		$ 15,000,000
Credit facility, commitment fee percentage		1.25%
Credit facility, fronting fee percentage		0.175%