Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2018
Income per share
Strike price of the warrant transactions (in dollars per share)	$ 80.9063				$ 80.9063		$ 80.9063
Numerator, dollars in thousands:
Net earnings	$ 34,667	$ 21,518	$ 32,727	$ 18,340	$ 56,185	$ 51,067
Denominator:
Weighted average shares outstanding, basic (in shares)	52,557,035		52,385,590		52,545,910	52,361,149
Effect of dilutive securities:
Stock options, RSU and SAR (in shares)	1,088,793		1,527,387		1,065,508	1,586,685
Weighted average shares outstanding, diluted (in shares)	53,645,828		53,912,977		53,611,418	53,947,834
Earnings per share, basic (in dollars per share)	$ 0.66		$ 0.62		$ 1.07	$ 0.98
Earnings per share, diluted (in dollars per share)	$ 0.65		$ 0.61		$ 1.05	$ 0.95
Stock options, RSUs, PSUs
Income per share
Common stock equivalents excluded in the calculation of diluted income per share (in shares)	2,999,885		1,030,370		3,022,165	300,342
2023 Notes
Income per share
Conversion price, per share of common stock (in dollars per share)	$ 59.33				$ 59.33		$ 59.33