Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities:
Net income	$ 76,598	$ 95,393	$ 70,119
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	37,764	31,029	35,029
Deferred income taxes	(8,843)	(711)	(11,103)
Gain on CRS settlement		(9,949)
Revaluation of derivatives		(490)	(1,039)
Debt extinguishment expenses			1,370
Stock compensation	9,186	6,018	4,652
Loss on sale of property and equipment	468	20	131
Loss from write-off of intangible assets		358
Provision for doubtful accounts	108	(120)	24
Defined benefit pension plan expense	184	668	820
Gain from equity investment			(785)
Changes in operating assets and liabilities:
Accounts receivable	(17,971)	(12,399)	(16,902)
Inventory	(5,933)	(10,954)	(8,367)
Prepaid expenses and other assets	9,106	(11,122)	(5,871)
Accounts payable	4,419	8,049	6,956
Accrued liabilities	3,314	8,922	5,301
Net cash provided by operating activities	108,400	104,712	80,335
Investing Activities:
Settlement of derivative financial instruments		(7,593)
Investment in subsidiary, net of cash acquired	(73,593)	107	(31,474)
Investment in development-stage entity	(4,486)
Purchases of property and equipment	(66,316)	(55,490)	(38,887)
Proceeds from the sale of property and equipment	57	248	487
Net cash used in investing activities	(144,338)	(62,728)	(69,874)
Financing Activities:
Cash paid for financing costs	(649)		(1,139)
Borrowing of Debt	115,000	15,000	91,592
Repayments of Debt	(42,244)	(5,053)	(79,692)
Cash paid for the cancellation of restricted stock	(1,196)	(1,475)	(1,113)
Excess tax benefit from equity awards	7,509	6,681	1,831
Proceeds from the exercise of Common Stock options	1,438	9,273	7,176
Net cash provided by financing activities	79,858	24,426	18,655
Foreign currency effect on cash and cash equivalents	(11,212)	(7,631)	1,699
Net increase in cash and cash equivalents	32,708	58,779	30,815
Cash and cash equivalents at beginning of period	144,479	85,700	54,885
Cash and cash equivalents at end of period	177,187	144,479	85,700
Supplemental disclosure of cash flow information:
Cash paid for interest	3,029	2,826	2,558
Cash paid for taxes	21,608	32,376	21,756
Supplemental disclosure of non-cash transactions:
Common Stock issued to directors and employees	$ 4,589	$ 3,734	$ 2,706