Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 32,637	$ 31,339
Weighted average shares outstanding: [Abstract]
Basic (in shares)	39,479	40,370
Effect of dilutive securities: [Abstract]
Stock options and employee stock purchase plan (in shares)	1,217	1,492
Diluted (in shares)	40,696	41,862
Basic (in dollars per share)	$ 0.83	$ 0.78
Diluted (in dollars per share)	$ 0.80	$ 0.75
Anti-dilutive stock options excluded from diluted earnings per share computations (in shares)	65	85