Employee Stock Benefit Plans (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding balance at beginning of period	645,223	656,671	834,010
Granted	249,392	351,590	108,297
Exercised	(33,389)	(100,813)	(241,122)
Canceled	(98,676)	(262,225)	(44,514)
Outstanding balance at end of period	762,550	645,223	656,671	834,010
Exercisable balance at end of period	333,761
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted-average exercise price, balance at beginning of period (in USD per share)	$ 19.17	$ 21.22	$ 17.28
Granted, weighted-average exercise price (in USD per share)	11.74	17.23	36.90
Exercised, weighted-average exercise price (in USD per share)	13.96	13.90	13.85
Canceled, weighted-average exercise price (in USD per share)	19.42	23.73	25.43
Outstanding, weighted-average exercise price, balance at end of period (in USD per share)	$ 16.91	$ 19.17	$ 21.22	$ 17.28
Outstanding, weighted-average remaining contractual life	6 years 11 months 23 days	6 years 7 months 24 days	6 years 10 months 2 days	6 years 7 months 28 days
Outstanding, aggregate intrinsic value	$ 64	$ 1,407	$ 2,103	$ 11,808
Exercised, aggregate intrinsic value	$ 17	$ 379	$ 5,722
Exercisable balance at end of period, weighted-average exercise price (in USD per share)	$ 19.26
Exercisable, weighted average remaining contractual life	4 years 9 months 7 days
Exercisable, aggregate intrinsic value	$ 35