Equity Incentive Plans - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Shares
Options outstanding, Beginning Balance, Shares | shares	1,462
Options granted, Shares | shares	391
Options exercised, Shares | shares	(78)
Options forfeited/canceled/expired, Shares | shares	(151)
Options outstanding, Ending Balance, Shares | shares	1,624	1,462
Options vested and expected to vest, ending balance, Shares | shares	1,538
Options exercisable, ending balance, Shares | shares	819
Wtd. Avg. Exercise Price
Options outstanding, Beginning Balance, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	$ 24.30
Options granted, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	22.68
Options exercised, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	16.03
Options forfeited/canceled/expired, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	24.48
Options outstanding, Ending Balance, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	24.31	$ 24.30
Options vested and expected to vest, ending balance, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	24.37
Options exercisable, ending balance, Wtd. Avg. Exercise Price (in dollars per share) | $ / shares	$ 24.88
Options, Additional Disclosures
Options outstanding, Remaining Contractual Term	7 years 2 months 1 day	7 years 2 months 12 days
Options vested and expected to vest, ending balance, Wtd. Avg., Remaining Contractual Term	7 years 29 days
Options exercisable, ending balance, Wtd. Avg. Remaining Contractual Term	5 years 9 months 18 days
Options outstanding, Aggregate Intrinsic Value | $	$ 314	$ 924
Options vested and expected to vest, ending balance, Aggregate Intrinsic Value | $	314
Options exercisable, ending balance, Aggregate Intrinsic Value | $	$ 314