Employee Stock Benefit Plans - Stock option activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Summary of stock option activity - Shares
Options outstanding at the beginning of the period (in shares) | shares	5,462,787
Granted (in shares) | shares	1,110,100
Exercised (in shares) | shares	(341,337)
Canceled (in shares) | shares	(558,747)
Expired (in shares) | shares	(838,548)
Options outstanding at the end of the period (in shares) | shares	4,834,255
Options exercisable at the end of the period (in shares) | shares	2,951,940
Summary of stock option activity - Weighted-Average Exercise Price (in dollars per share)
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 36.88
Granted (in dollars per share) | $ / shares	19.88
Exercised (in dollars per share) | $ / shares	8.40
Canceled (in dollars per share) | $ / shares	33.91
Expired (in dollars per share) | $ / shares	40.59
Options outstanding at the end of the period (in dollars per share) | $ / shares	34.69
Options exercisable at the end of the period (in dollars per share) | $ / shares	$ 39.49
Weighted-Average Contractual Life (In Years)
Options outstanding at the end of the period	6 years 9 months 3 days
Options exercisable at the end of the period	5 years 6 months 21 days
Aggregate Intrinsic Value
Options outstanding at the end of the period | $	$ 4,167
Options exercisable at the end of the period | $	$ 3,166