Employee Benefits and Share-Based Compensation - Stock Options and ESPP Shares (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life, years	4 years 9 months 15 days	4 years 8 months 1 day	4 years 10 months 24 days
Expected volatility, %	31.10%	29.60%	30.60%
Risk-free interest rate, %	2.80%	1.90%	1.50%
Estimated forfeiture rate, %	6.90%	7.70%	8.60%
Dividend yield, %	0.00%	0.00%	0.00%
2009 Plan | Employee Stock Option
Number of Shares
Outstanding at beginning of year (in shares)	3,323
Granted (in shares)	1,359
Exercised (in shares)	(672)
Expired (in shares)	(16)
Forfeited (in shares)	(246)
Outstanding at end of year (in shares)	3,748	3,323
Exercisable (in shares)	1,397
Vested and expected to vest (in shares)	3,532
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 32.72
Granted (in dollars per share)	54.00
Exercised (in dollars per share)	25.68
Expired (in dollars per share)	26.54
Forfeited (in dollars per share)	39.60
Outstanding at end of year (in dollars per share)	41.27	$ 32.72
Exercisable (in dollars per share)	29.69
Vested and expected to vest (in dollars per share)	$ 40.64
Weighted-Average Remaining Years	7 years 7 months 17 days	7 years 7 months 13 days
Exercisable (in years)	5 years 8 months 12 days
Vested and expected to vest (in years)	7 years 7 months 6 days
Outstanding Aggregate Intrinsic Value	$ 78,365	$ 53,953
Exercisable Aggregate Intrinsic Value	44,084
Vested and expected to vest Aggregate Intrinsic Value	$ 75,823
Weighted-average fair value (in usd per share)	$ 17.22	$ 13.25	$ 9.33
Intrinsic value of options exercised	$ 20,100	$ 18,200	$ 5,600
Unrecognized compensation cost of unvested stock options	$ 29,700
Weighted average period of compensation cost recognized (in years)	2 years 10 months 17 days
1997 Employee Stock Purchase Plan | Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield, %	0.00%	0.00%	0.00%
Weighted-Average Exercise Price
Weighted average period of compensation cost recognized (in years)	1 year 3 months
Shares purchased under ESPP	500
Shares issued under ESPP	6,400
Unrecognized compensation cost	$ 3,900