Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Cash Flows [Abstract]
Net income	$ 44,090	$ 37,333
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,407	2,194
Amortization of debt issuance costs	30	30
Stock-based compensation	1,290	447
Loss on disposal of fixed assets	384	13
Deferred income taxes	2,484	11,373
Tax benefit from exercise of stock options	0	(3)
Payment of class action legal settlement	0	(32,000)
Effect of changes in operating assets and liabilities:
Receivables	5,461	16,387
Inventories	(9,545)	7,306
Prepaid expenses and other assets	1,112	1,740
Accounts payable	4,272	1,970
Other liabilities	1,383	(4,257)
Net cash provided by operating activities	53,368	42,533
Cash flows from investing activities:
Capital expenditures	(8,362)	(796)
Net cash used in investing activities	(8,362)	(796)
Cash flows from financing activities:
Principal payments on long-term debt	(990)	(990)
Proceeds from exercise of stock options	1,426	61
Tax benefit from exercise of stock options	0	3
Net cash provided by (used in) financing activities	436	(926)
Effect of exchange rate changes on cash and cash equivalents	134	23
Net increase in cash and cash equivalents	45,576	40,834
Cash and cash equivalents at beginning of period	292,656	224,253
Cash and cash equivalents at end of period	$ 338,232	$ 265,087