Equity Incentive Plans - Options by Exercise Price (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Granted, Wtd. Avg. grant date fair value (in dollars per share)	$ 3.64	$ 5.91	$ 2.09
Options granted, shares	475	500	300
Exercise prices and related information of stock option outstanding
Options outstanding, number outstanding (in shares)	1,462
Options outstanding, Wtd. Avg. remaining contractual life	7 years 1 month 43 days
Options outstanding, Wtd. Avg. exercise price (in dollars per share)	$ 24.30
Options exercisable, Number exercisable (in shares)	646
Options exercisable Wtd. Avg. Remaining Contractual Life	5 years 7 months 4 days
Options exercisable, Wtd. Avg. exercise price (in dollars per share)	$ 23.81
0-18.23
Exercise prices and related information of stock option outstanding
Lower range limit, Exercise price (in dollars per share)	0
Upper range limit, Exercise price (in dollars per share)	$ 18.23
Options outstanding, number outstanding (in shares)	161
Options outstanding, Wtd. Avg. remaining contractual life	2 years 3 months 25 days
Options outstanding, Wtd. Avg. exercise price (in dollars per share)	$ 14.08
Options exercisable, Number exercisable (in shares)	160
Options exercisable Wtd. Avg. Remaining Contractual Life	2 years 3 months 25 days
Options exercisable, Wtd. Avg. exercise price (in dollars per share)	$ 14.08
18.24-22.26
Exercise prices and related information of stock option outstanding
Lower range limit, Exercise price (in dollars per share)	18.24
Upper range limit, Exercise price (in dollars per share)	$ 22.26
Options outstanding, number outstanding (in shares)	708
Options outstanding, Wtd. Avg. remaining contractual life	8 years 1 month 30 days
Options outstanding, Wtd. Avg. exercise price (in dollars per share)	$ 20.98
Options exercisable, Number exercisable (in shares)	169
Options exercisable Wtd. Avg. Remaining Contractual Life	6 years 33 days
Options exercisable, Wtd. Avg. exercise price (in dollars per share)	$ 20.54
22.27-29.39
Exercise prices and related information of stock option outstanding
Lower range limit, Exercise price (in dollars per share)	22.27
Upper range limit, Exercise price (in dollars per share)	$ 29.39
Options outstanding, number outstanding (in shares)	218
Options outstanding, Wtd. Avg. remaining contractual life	6 years 1 month 10 days
Options outstanding, Wtd. Avg. exercise price (in dollars per share)	$ 28.77
Options exercisable, Number exercisable (in shares)	165
Options exercisable Wtd. Avg. Remaining Contractual Life	6 years 33 days
Options exercisable, Wtd. Avg. exercise price (in dollars per share)	$ 28.77
29.40-43.15
Exercise prices and related information of stock option outstanding
Lower range limit, Exercise price (in dollars per share)	32.41
Upper range limit, Exercise price (in dollars per share)	$ 43.15
Options outstanding, number outstanding (in shares)	375
Options outstanding, Wtd. Avg. remaining contractual life	8 years 30 days
Options outstanding, Wtd. Avg. exercise price (in dollars per share)	$ 32.27
Options exercisable, Number exercisable (in shares)	152
Options exercisable Wtd. Avg. Remaining Contractual Life	7 years 9 months 70 days
Options exercisable, Wtd. Avg. exercise price (in dollars per share)	$ 32.27