Condensed Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Thousands	Total	Common Stock	Additional  Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings
Balance (in shares) at Dec. 31, 2018		52,316,583
Balance at Dec. 31, 2018	$ 453,023	$ 52	$ 369,637	$ (3,158)	$ 86,492
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,287		3,287
Exercise of stock options (in shares)		57,665
Exercise of stock options	783		783
Net earnings	18,340				18,340
Unrealized gain on marketable securities, net of tax	4,585			4,585
Balance (in shares) at Mar. 31, 2019		52,374,248
Balance at Mar. 31, 2019	480,018	$ 52	373,707	1,427	104,832
Balance (in shares) at Dec. 31, 2018		52,316,583
Balance at Dec. 31, 2018	453,023	$ 52	369,637	(3,158)	86,492
Increase (Decrease) in Stockholders' Equity
Net earnings	51,067
Unrealized gain on marketable securities, net of tax	9,082
Balance (in shares) at Jun. 30, 2019		52,449,036
Balance at Jun. 30, 2019	522,904	$ 52	379,369	5,924	137,559
Balance (in shares) at Mar. 31, 2019		52,374,248
Balance at Mar. 31, 2019	480,018	$ 52	373,707	1,427	104,832
Increase (Decrease) in Stockholders' Equity
Share-based compensation	4,022		4,022
Issuance of ESPP shares (in shares)		48,950
Issuance of ESPP shares	1,377		1,377
Exercise of stock options (in shares)		25,838
Exercise of stock options	263		263
Net earnings	32,727				32,727
Unrealized gain on marketable securities, net of tax	4,497			4,497
Balance (in shares) at Jun. 30, 2019		52,449,036
Balance at Jun. 30, 2019	522,904	$ 52	379,369	5,924	137,559
Balance (in shares) at Dec. 31, 2019		52,533,348
Balance at Dec. 31, 2019	595,428	$ 53	388,410	7,417	199,548
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,988		3,988
Exercise of stock options (in shares)		3,811
Exercise of stock options	32		32
Net earnings	21,518				21,518
Unrealized gain on marketable securities, net of tax	(7,583)			(7,583)
Balance (in shares) at Mar. 31, 2020		52,537,159
Balance at Mar. 31, 2020	613,383	$ 53	392,430	(166)	221,066
Balance (in shares) at Dec. 31, 2019		52,533,348
Balance at Dec. 31, 2019	595,428	$ 53	388,410	7,417	199,548
Increase (Decrease) in Stockholders' Equity
Net earnings	56,185
Unrealized gain on marketable securities, net of tax	3,942
Balance (in shares) at Jun. 30, 2020		52,624,084
Balance at Jun. 30, 2020	665,974	$ 53	398,829	11,359	255,733
Balance (in shares) at Mar. 31, 2020		52,537,159
Balance at Mar. 31, 2020	613,383	$ 53	392,430	(166)	221,066
Increase (Decrease) in Stockholders' Equity
Share-based compensation	4,962		4,962
Issuance of ESPP shares (in shares)		48,650
Issuance of ESPP shares	981		981
Exercise of stock options (in shares)		38,275
Exercise of stock options	456		456
Net earnings	34,667				34,667
Unrealized gain on marketable securities, net of tax	11,525			11,525
Balance (in shares) at Jun. 30, 2020		52,624,084
Balance at Jun. 30, 2020	$ 665,974	$ 53	$ 398,829	$ 11,359	$ 255,733