Long-term Debt and Line of Credit - Provisions of the Revolving Line of Credit and Accordion (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 05, 2015
Debt Instrument [Line Items]
Repayments of debt		$ 48,111,000	$ 87,813,000	$ 63,084,000
Proceeds from lines of credit		39,861,000	$ 72,000,000	$ 57,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$ 22,000,000	22,000,000
Remaining borrowing capacity	42,200,000	42,200,000
Repayments of debt	39,900,000
Proceeds from lines of credit		39,900,000
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 65,000,000.0	$ 65,000,000.0			$ 100,000,000.0
Minimum additional borrowing amount					1,000,000
Amount over minimum additional borrowing amount, integral multiples					250,000
Stated interest rate	4.63%	4.63%
Revolving Credit Facility | Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					20,000,000
Letters of credit outstanding	$ 800,000	$ 800,000
Revolving Credit Facility | Bridge Loan
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					5,000,000
Minimum additional borrowing amount					250,000
Amount over minimum additional borrowing amount, integral multiples					$ 50,000
Term Loan | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	60,000,000.0	60,000,000.0
Line of credit facility, amount outstanding	$ 58,500,000	58,500,000
Repayments of debt		$ 12,000,000