Long-term Debt, Line of Credit and Derivatives - Provisions of the revolving line of credit and accordion (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Aug. 05, 2015
Debt Instrument [Line Items]
Repayments of debt		$ 74,438,000	$ 42,552,000
Proceeds from Lines of Credit		$ 52,000,000	$ 47,000,000
Line of Credit
Debt Instrument [Line Items]
Interest rate				4.75%
Weighted average interest rate	3.80%	3.80%
Revolving line of credit
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity	$ 49,100,000	$ 49,100,000
Repayments of debt	15,000,000
Proceeds from Lines of Credit	20,000,000
Revolving line of credit | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 50,000,000
Minimum additional borrowing amount				1,000,000
Amount over minimum additional borrowing amount, integral multiples				250,000
Revolving line of credit | Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				20,000,000
Letters of credit outstanding, amount	900,000	900,000
Revolving line of credit | 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	135,000,000	135,000,000
Fair value of amount outstanding	$ 82,100,000	82,100,000
Repayments of debt		$ 3,000,000
Term Loan | Line of Credit | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate, effective percentage	3.75%	3.75%