Summary of Significant Accounting Policies - Reconciliation of Effects of Reclassification on Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales	$ 427,433	$ 290,465	$ 796,746	$ 535,262
Product cost of sales	236,236	162,238	443,475	324,134
Service cost of sales	56,609	34,726	110,280	60,018
Total cost of sales (excluding depreciation, depletion and amortization)	292,845	196,964	553,755	384,152
Selling, general and administrative expenses	42,232	25,839	76,823	47,978
Operating income	39,609	44,036	84,829	57,907
Other income (expense)	1,081	638	1,746	(4,779)
Product
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales	345,957	235,891	640,745	439,143
Service
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales	$ 81,476	54,574	$ 156,001	96,119
As Previously Reported
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		290,465		535,262
Product cost of sales		164,025		326,662
Service cost of sales		33,386		58,224
Total cost of sales (excluding depreciation, depletion and amortization)		197,411		384,886
Selling, general and administrative expenses		26,012		48,353
Operating income		43,416		56,798
Other income (expense)		1,258		(3,670)
As Previously Reported | Product
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		246,022		455,343
As Previously Reported | Service
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		44,443		79,919
ASU 2017-07 Adjustments
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		0		0
Product cost of sales		(1,340)		(1,794)
Service cost of sales		1,340		1,794
Total cost of sales (excluding depreciation, depletion and amortization)		0		0
Selling, general and administrative expenses		0		0
Operating income		0		0
Other income (expense)		0		0
ASU 2017-07 Adjustments | Product
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		(10,131)		(16,200)
ASU 2017-07 Adjustments | Service
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		10,131		16,200
ASU 2017-07 Adjustments | Accounting Standards Update 2017-07
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		0		0
Product cost of sales		(447)		(734)
Service cost of sales		0		0
Total cost of sales (excluding depreciation, depletion and amortization)		(447)		(734)
Selling, general and administrative expenses		(173)		(375)
Operating income		620		1,109
Other income (expense)		(620)		(1,109)
ASU 2017-07 Adjustments | Accounting Standards Update 2017-07 | Product
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		0		0
ASU 2017-07 Adjustments | Accounting Standards Update 2017-07 | Service
New Accounting Pronouncement, Early Adoption [Line Items]
Total Sales		$ 0		$ 0