Stock-Based Compensation (Stock Option Activity) (Details) - Stock Options shares in Thousands	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Number of Shares
Options outstanding at the beginning of the period (in shares) | shares	3,460
Options granted (in shares) | shares	599
Options exercised (in shares) | shares	(65)
Options forfeited (in shares) | shares	(77)
Options outstanding at the end of the period (in shares) | shares	3,917
Exercisable at the end of the period (in shares) | shares	2,493
Vested and expected to vest at the end of the period (in shares) | shares	3,799
Weighted-Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 26.42
Options granted (in dollars per share) | $ / shares	33.21
Options exercised (in dollars per share) | $ / shares	17.66
Options forfeited (in dollars per share) | $ / shares	29.44
Options outstanding at the end of the period (in dollars per share) | $ / shares	27.54
Exercisable at the end of the period (in dollars per share) | $ / shares	26.02
Vested and expected to vest at the end of the period (in dollars per share) | $ / shares	$ 27.44