Debt and Credit Agreement - Rollforward of 2016 new debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Amortization of debt financing fees	$ 1,590	$ 0	$ 0
Long term debt, current portion, net of deferred issuance cost	8,410	0
Long term debt, net of deferred issuance cost	245,731	0
Wells Fargo Bank, National Association
Debt Instrument [Line Items]
Long-term Line of Credit, Gross	260,500	0
Proceeds from debt	295,000
Repayment of debt and revolving credit facility	(34,500)
Debt issuance cost, net	(6,359)	0
Debt issuance cost, gross	(7,949)
Amortization of debt financing fees	1,590
Long-term Debt	254,141	0
Proceeds from Long-term Lines of Credit, Net of Financing Costs	287,051
Repayments of Lines of Credit, Net of Financing Costs	32,910
Long term debt, current portion, net of deferred issuance cost	8,410
Long term debt, net of deferred issuance cost	245,731
Term Loan Facility | Wells Fargo Bank, National Association
Debt Instrument [Line Items]
Long-term Line of Credit, Gross	192,500	0
Proceeds from debt	200,000
Repayment of debt and revolving credit facility	(7,500)
Revolving Credit Facility | Wells Fargo Bank, National Association
Debt Instrument [Line Items]
Long-term Line of Credit, Gross	68,000	$ 0
Proceeds from debt	95,000
Repayment of debt and revolving credit facility	$ (27,000)