Long-Term Debt (Narrative) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Amount outstanding under revolving credit facility	$ 70,090,000	$ 144,083,000
2017	73,000
2018	17,000
2019	0
2020	0
Thereafter	70,000,000
Amended and Restated Revolving Credit Agreement | Bank revolving credit facility | Unsecured Debt
Debt Instrument [Line Items]
Aggregate commitments	250,000,000
Maximum amount of aggregate commitments	50,000,000
Amount outstanding under revolving credit facility	70,000,000	$ 144,000,000
Available borrowings	178,286,000
Amended and Restated Revolving Credit Agreement | Standby Letters of Credit | Unsecured Debt
Debt Instrument [Line Items]
Amount of capacity	$ 1,714,000