Share-Based Payments - Stock Option Activity (Details) - Stock options $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at the beginning of the period (in shares) | shares	7,009
Granted (in shares) | shares	1,531
Exercised (in shares) | shares	(803)
Forfeited (in shares) | shares	(369)
Expired (in shares) | shares	(251)
Outstanding at the end of the period (in shares) | shares	7,117
Exercisable at the end of the period (in shares) | shares	4,575
Vested and expected to vest at the end of the period (in shares) | shares	6,854
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 13.68
Granted (in dollars per share) | $ / shares	17.88
Exercised (in dollars per share) | $ / shares	11.46
Forfeited (in dollars per share) | $ / shares	14.10
Expired (in dollars per share) | $ / shares	16.55
Outstanding at the end of the period (in dollars per share) | $ / shares	14.71
Exercisable at the end of the period (in dollars per share) | $ / shares	14.23
Vested and expected to vest at the end of the period (in dollars per share) | $ / shares	$ 14.65
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding at the end of the period	5 years 10 months 2 days
Exercisable at the end of the period	4 years 6 months 18 days
Vested and expected to vest at the end of the period	5 years 8 months 27 days
Outstanding at the end of the period (in thousands) | $	$ 6,751
Exercisable at the end of the period (in thousands) | $	4,593
Vested and expected to vest at the end of the period (in thousands) | $	$ 6,594