Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 193,529	$ 130,241	$ 89,388
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	10,514	9,200	8,170
Amortization of debt issuance costs	354	122	122
Stock-based compensation	3,683	4,609	3,434
Deferred compensation	0	0	19
Loss on disposal of fixed assets	593	49	89
Deferred income taxes	(4,306)	11,988	(12,071)
Income tax benefit from exercise of stock options	0	0	(1,536)
Provision for class action legal settlement	0	0	32,000
Payment for class action legal settlement	0	(32,000)	0
Effect of changes in operating assets and liabilities:
Receivables	(33,611)	(35,509)	(1,487)
Inventories	(8,930)	12,493	5,140
Prepaid expenses and other assets	(1,928)	(2,109)	(1,189)
Accounts payable	27,995	4,563	(1,733)
Other liabilities	5,966	23,596	17,873
Net cash provided by operating activities	193,859	127,243	138,219
Cash flows from investing activities:
Capital expenditures	(170,970)	(56,345)	(9,556)
Restricted cash	0	(308)	0
Proceeds from the sale of fixed assets	0	15	0
Net cash used in investing activities	(170,970)	(56,638)	(9,556)
Cash flows from financing activities:
Proceeds from issuance of debt	400,000	0	0
Repayment of long-term debt	(382,147)	0	0
Repurchase of common stock	(50,000)	0	0
Payment of debt issuance costs	(4,352)	0	0
Principal payments on long-term debt	(2,990)	(3,960)	(3,960)
Income tax benefit from exercise of stock options, financing activities	0	0	1,536
Proceeds from exercise of stock options	6,021	1,915	2,251
Net Cash Provided by (Used in) Financing Activities	(33,468)	(2,045)	(173)
Effect of Exchange Rate on Cash and Cash Equivalents	146	(157)	(25)
Cash and Cash Equivalents, Period Increase (Decrease)	(10,433)	68,403	128,465
Cash and Cash Equivalents	282,223	292,656	224,253
Accruals related to property, plant and equipment	$ 5,411	$ 0	$ 0