Stock-Based Compensation - Stock Award Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee And Non Employee Stock Option
Stock option activity
Total options outstanding, beginning of period (in shares)	4,951,256	5,968,763	5,893,241
Granted (in shares)	215,500	1,262,500	732,000
Exercised (in shares)	(108,318)	(1,018,507)	(453,182)
Forfeited and canceled (in shares)	(45,400)	(1,261,500)	(203,296)
Total options outstanding, end of period (in shares)	5,013,038	4,951,256	5,968,763
Exercisable at end of period (in shares)	3,710,138	3,143,656	3,551,063
Weighted-Average Exercise Price
Total options outstanding, beginning of period (in dollars per share)	$ 41.42	$ 39.30	$ 38.38
Granted (in dollars per share)	51.71	57.12	41.86
Exercised (in dollars per share)	40.67	35.84	28.83
Forfeited and canceled (in dollars per share)	50.21	51.63	45.15
Total options outstanding, end of period (in dollars per share)	41.80	41.42	39.30
Exercisable at end of period (in dollars per share)	$ 38.59	$ 36.98	$ 35.40
Restricted stock units
Restricted stock unit activity
Total restricted stock units outstanding, beginning of period (in shares)	0	6,667	57,328
Vested (in shares)	0	(6,667)	(50,661)
Total restricted stock units outstanding, end of period (in shares)	0	0	6,667
Weighted - Average Grant Date Fair Value
Total restricted stock units outstanding, beginning of period (in dollars per share)	$ 0	$ 34.22	$ 42.31
Vested (in dollars per share)	0	34.22	43.38
Total restricted stock units outstanding, end of period (in dollars per share)	$ 0	$ 0	$ 34.22