Condensed Consolidated Statements of Cash Flows (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash Flows from Operating Activities:
Net income	$ 7,755,355	$ 7,246,065
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,948,266	3,395,443
(Gain) loss on write down / disposal of property and equipment, net	(28,960)	106,824
Loss on disposal of intangibles	110,993	71,351
Bond premium amortization	68,766	35,812
Provision for doubtful accounts	479	481
Provision for excess and obsolete inventory	168,973	197,468
Provision for warranty	505,852	97,226
Stock-based compensation expense	1,942,641	1,347,662
Litigation judgment recovery		(2,200,000)
Deferred income taxes	3,799,192	3,185,099
Provision for unrecognized tax benefits	169,967	29,967
Excess tax benefit from stock-based compensation	(3,879,575)
Change in assets and liabilities:
Accounts and notes receivable	1,210,976	(2,916,419)
Inventory	(2,376,200)	820,435
Prepaids and other assets	(3,776,541)	(8,646)
Accounts payable and accrued liabilities	(600,333)	397,322
Deferred revenue	3,468,250	1,260,534
Customer deposits	735,168	317,882
Net cash provided by operating activities	12,223,269	13,384,506
Cash Flows from Investing Activities:
Purchases of investments	(12,676,780)	(6,242,033)
Proceeds from call / maturity of investments	1,680,000	6,128,147
Purchases of property and equipment	(838,995)	(602,302)
Proceeds from disposal of fixed assets	33,709
Purchases of intangible assets	(202,193)	(251,987)
Net cash used in investing activities	(12,004,259)	(968,175)
Cash Flows from Financing Activities:
Repurchase of common stock	(24,999,767)	(16,138,551)
Proceeds from options exercised	4,050,734	396,885
Payroll tax payments for net-settled stock awards	(185,317)
Excess tax benefit from stock-based compensation	3,879,575
Payments on capital lease obligation	(16,711)
Net cash used in financing activities	(17,271,486)	(15,741,666)
Effect of exchange rate change on cash and cash equivalents	5,026	(5,379)
Net decrease in cash and cash equivalents	(17,047,450)	(3,330,714)
Cash and cash equivalents, beginning of period	36,126,791	21,300,733
Cash and cash equivalents, end of period	19,079,341	17,970,019
Supplemental Disclosure:
Cash paid for income taxes-net	2,291,762	820,361
Non-Cash Transactions:
Property and equipment purchases in accounts payable	$ 51,257	$ 47,955