Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 231,681	$ 262,476	$ 263,002	$ 219,866	$ 200,192	$ 230,974	$ 229,973	$ 199,523	$ 977,025	$ 860,661	$ 794,059
Cost of sales	128,983	142,591	139,477	119,710	105,226	117,499	118,486	107,000	530,761	448,211	435,140
Gross profit	102,698	119,885	123,525	100,156	94,966	113,475	111,487	92,523	446,264	412,450	358,919
Research and development and other engineering	12,565	8,679	13,264	13,108	12,441	10,932	11,452	11,423	47,616	46,248	46,196
Selling	28,753	28,156	28,511	29,483	24,030	24,304	24,822	25,187	114,903	98,343	90,663
General and administrative	36,688	36,501	36,563	34,986	32,376	32,543	34,945	29,298	144,738	129,162	113,428
Gain (loss) on sale of assets	(13)	(147)	50	(50)	(17)	(81)	(656)	(26)	(160)	(780)	(389)
Income from operations	24,705	46,696	45,137	22,629	26,136	45,777	40,924	26,641	139,167	139,477	109,021
Loss in equity method investment, before tax	(33)	(13)	(12)	(28)					(86)	0	0
Interest income, net	(104)	(296)	(199)	(189)	(177)	(82)	(83)	(235)
Gain (loss) on bargain purchase of a business (adjustment)	0	(2,052)	0	8,388
Loss on disposal of a business	(654)	443	0	0					(211)	0	0
Income before taxes									144,418	138,900	108,679
Provision for (benefit from) income taxes	10,829	16,581	16,712	7,679	8,565	15,898	14,640	10,063	51,801	49,166	40,791
Net income	$ 13,085	$ 28,197	$ 28,214	$ 23,121	$ 17,394	$ 29,797	$ 26,201	$ 16,343	$ 92,617	$ 89,734	$ 67,888
Earnings per share of common stock:
Basic (in USD per share)	$ 0.28	$ 0.60	$ 0.59	$ 0.49	$ 0.37	$ 0.62	$ 0.54	$ 0.34	$ 1.95	$ 1.87	$ 1.39
Diluted (in USD per share)	0.27	0.59	0.59	0.48	0.36	0.62	0.54	0.34	1.94	1.86	1.38
Cash dividends declared per common share (in dollars per share)	$ 0	$ 0.42	$ 0.21	$ 0.18	$ 0.18	$ 0.180	$ 0.180	$ 0.160	$ 0.81	$ 0.70	$ 0.62

Business Combination, Bargain Purchase, Gain (Loss) Recognized, Amount

No definition available.

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Namespace Prefix:	ssd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use; (3) to conduct internal product testing; (4) or to provide engineering support to customers in the form of testing services or product uses, specifications or requirements.

+ References

No definition available.