Convertible Subordinated Notes (Details) - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Mar. 19, 2014
Debt Instrument [Line Items]
Effect of dilutive securities, Convertible junior subordinated debentures (in shares)	787	299	980	200
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Debt issuance costs	$ (1,043,000)		$ (1,043,000)		$ (1,270,000)
Accumulated Amortization, Debt Issuance Costs	4,366,000		4,366,000		4,138,000
Amortization of Debt Issuance Costs			614,000	$ 622,000
Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Stated interest rate percentage						2.75%
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Convertible subordinated notes, principal amount	143,750,000		143,750,000		143,750,000	$ 143,750,000
Unamortized discount of liability component	(18,687,000)		(18,687,000)		(21,887,000)
Debt issuance costs	(1,881,000)		(1,881,000)		(2,268,000)
Accumulated Amortization, Debt Issuance Costs	1,746,000		1,746,000		1,359,000
Carrying value of the liability component	123,182,000		123,182,000		119,596,000
Equity component carrying value	17,973,000		17,973,000		$ 17,973,000
Convertible subordinated notes, fair value	179,900,000		179,900,000
Contractual coupon interest expense	1,000,000	$ 1,000,000	3,000,000	3,000,000
Accretion of discount, convertible subordinated notes	$ 1,100,000	$ 1,000,000	$ 3,200,000	$ 2,900,000
Effective interest rate percentage	2.75%	6.75%	2.75%	6.75%
Amortization of Debt Issuance Costs	$ 100,000	$ 100,000	$ 400,000	$ 400,000