Convertible Subordinated Notes Convertible Subordinated Notes (Narrative) (Details) (Details) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended
	Jun. 30, 2017	Mar. 19, 2014 $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Amortization of Debt Issuance Costs					$ 614	$ 622
Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Conversion Ratio	44.5392	44.3169
Long-term Debt, Fair Value			$ 179,900		179,900
Interest Expense, Debt			1,000	$ 1,000	3,000	3,000
Amortization of Debt Issuance Costs			100	100	400	400
Accretion of discount, convertible subordinated notes			$ 1,100	$ 1,000	$ 3,200	$ 2,900
Debt instrument, convertible, conversion price (in dollars per share) | $ / shares		$ 22.56	$ 22.45		$ 22.45
Effective interest rate percentage			2.75%	6.75%	2.75%	6.75%