Long-term Debt, Line of Credit and Derivatives - Obligations under Debt Arrangements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Aug. 05, 2015
Debt Instrument [Line Items]
Debt issuance costs	$ 900
Debt issuance expense	700
Principal, current	3,000	$ 3,000
Principal, long-term	77,500	77,750
Principal	80,500	80,750
Deferred Issuance Costs, current	(54)	(50)
Deferred Issuance Costs, long-term	(1,381)	(1,258)
Deferred Issuance Costs	(1,435)	(1,308)
Net Value, current	2,946	2,950
Net Value, long-term	76,119	76,492
Total debt	79,065	79,442
Term Loan | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	60,000
Total debt		$ 57,750
Revolving line of credit | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	65,000		$ 100,000
Stated interest rate		5.25%
Principal, long-term	22,000	$ 23,000
Deferred Issuance Costs, long-term	(213)	(372)
Net Value, long-term	21,787	22,628
Term loan - current | Loans Payable
Debt Instrument [Line Items]
Principal, current	3,000	3,000
Deferred Issuance Costs, current	(54)	(50)
Net Value, current	2,946	2,950
Term loan - long-term | Loans Payable
Debt Instrument [Line Items]
Principal, long-term	55,500	54,750
Deferred Issuance Costs, long-term	(1,168)	(886)
Net Value, long-term	$ 54,332	$ 53,864