Employee Benefits and Share-Based Compensation - Performance Based Restricted Stock Unit Activity (Details) - 2009 Plan - Performance Shares $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Number of Shares
Outstanding at beginning of period (in shares) | shares	197
Granted (in shares) | shares	71
Vested (in shares) | shares	(58)
Canceled (in shares) | shares	(33)
Outstanding and unvested at end of period (in shares) | shares	177
Weighted-Average Grant Date Fair Value Per Share
Outstanding and unvested (in dollars per share) | $ / shares	$ 34.83
Granted (in dollars per share) | $ / shares	73.38
Vested (in dollars per share) | $ / shares	34.38
Canceled (in dollars per share) | $ / shares	33.84
Outstanding and unvested (in dollars per share) | $ / shares	$ 50.67
Unrecognized compensation cost | $	$ 4.9
Weighted average period of compensation cost not yet recognized (in years)	1 year 6 months