Stock-Based Compensation - Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options (in 000's)
Outstanding at beginning of the year (in shares)	652	648	650
Granted (in shares)	92	243	77
Exercised (in shares)	(56)	(239)	(71)
Forfeited/canceled/expired (in shares)	(168)	0	(8)
Outstanding at end of the year (in shares)	520	652	648
Vested and expected to vest at the end of the year (in shares)	520	652	648
Exercisable at the end of the year (in shares)	381	363	493
Weighted-Average Exercise Price
Outstanding at beginning of the year (in dollars per share)	$ 39.27	$ 30.50	$ 25.56
Granted (in dollars per share)	62.70	49.67	64.81
Exercised (in dollars per share)	25.72	26.09	23.97
Forfeited/canceled/expired (in dollars per share)	46.44	0.00	20.64
Outstanding at end of the year (in dollars per share)	42.56	39.27	30.50
Vested and expected to vest at the end of the year (in dollars per share)	42.56	39.27	30.50
Exercisable at the end of the year (in dollars per share)	$ 36.39	$ 30.21	$ 25.03
Weighted-Average Remaining Contractual Term and Aggregate Intrinsic Value
Outstanding at end of the year, term	4 years 3 months	4 years 9 months 10 days	4 years 10 months 6 days
Vested and expected to vest at the end of the year, term	4 years 3 months	4 years 9 months 10 days	4 years 10 months 6 days
Exercisable at the end of the year, term	3 years 8 months 19 days	3 years 10 months 17 days	4 years 6 months 3 days
Exercised	$ 2,140	$ 9,933	$ 2,193
Outstanding at end of the year	5,607	16,553	14,556
Vested and expected to vest at the end of the year	5,607	16,548	14,551
Exercisable at the end of the year	$ 5,607	$ 12,511	$ 12,979