Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Aug. 20, 2018
Earnings Per Common Share [Line Items]
Conversion price (in dollars per share)	$ 101.38
Numerator — basic and diluted
Net income	$ 62,645	$ 38,945
Denominator
Weighted average number of common shares outstanding — basic (in shares)	36,981	36,700
Effect of dilutive stock options (in shares)	431	303
Effect of dilutive restricted shares (in shares)	807	609
Weighted average number of common shares outstanding — diluted (in shares)	38,219	37,612
Earnings per common share — basic (in dollars per share)	$ 1.69	$ 1.06
Earnings per common share — diluted (in dollars per share)	$ 1.64	$ 1.04
Stock Options And Restricted Shares
Denominator
Antidilutive stock options and restricted shares (in shares)	49	613
Senior Notes | Convertible Note Due 2023
Earnings Per Common Share [Line Items]
Interest rate (as a percent)	2.00%
Conversion price (in dollars per share)			$ 101.38