Equity Incentive Plans - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Shares
Options outstanding, Beginning Balance, Shares	1,230
Options granted, Shares	475
Options exercised, Shares	(97)
Options forfeited/canceled/expired, Shares	(108)
Options outstanding, Ending Balance, Shares	1,500	1,230
Options vested and expected to vest, ending balance, Shares	1,404
Options exercisable, ending balance, Shares	656
Wtd. Avg. Exercise Price
Options outstanding, Beginning Balance, Wtd. Avg. Exercise Price (in dollars per share)	$ 25.02
Options granted, Wtd. Avg. Exercise Price (in dollars per share)	21.60
Options exercised, Wtd. Avg. Exercise Price (in dollars per share)	19.13
Options forfeited/canceled/expired, Wtd. Avg. Exercise Price (in dollars per share)	25.24
Options outstanding, Ending Balance, Wtd. Avg. Exercise Price (in dollars per share)	24.30	$ 25.02
Options vested and expected to vest, ending balance, Wtd. Avg. Exercise Price (in dollars per share)	24.31
Options exercisable, ending balance, Wtd. Avg. Exercise Price (in dollars per share)	$ 23.80
Options, Additional Disclosures
Options outstanding, Remaining Contractual Term	7 years 5 months 30 days	7 years 3 months 29 days
Options vested and expected to vest, ending balance, Wtd. Avg., Remaining Contractual Term	7 years 4 months 20 days
Options exercisable, ending balance, Wtd. Avg. Remaining Contractual Term	5 years 9 months 65 days
Options outstanding, Aggregate Intrinsic Value	$ 4,849	$ 3,117
Options vested and expected to vest, ending balance, Aggregate Intrinsic Value	4,580
Options exercisable, ending balance, Aggregate Intrinsic Value	$ 2,601