Nature of Business and Significant Accounting Policies (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 171,597	$ 282,425	$ 107,223
Denominator for earnings per share:
Weighted average number of common shares outstanding	135,016	137,815	137,456
Assumed exercise of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	1,621	2,394	2,190
Diluted shares outstanding	136,637	140,209	139,646