Nature of Business and Significant Accounting Policies (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 212,584	$ 171,597	$ 282,425
Denominator for earnings per share:
Weighted average number of common shares outstanding	131,648	135,016	137,815
Assumed exercise of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	941	1,621	2,394
Diluted shares outstanding	132,589	136,637	140,209