Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current [Abstract]
Federal	$ 27,985,000	$ 20,843,000	$ 0
State	4,145,000	4,232,000	2,704,000
Foreign	0	0
Total	32,130,000	25,075,000	2,704,000
Deferred [Abstract]
Federal	(3,050,000)	(504,000)	(460,000)
State	2,051,000	(911,000)	(3,951,000)
Foreign	(598,000)	(1,538,000)
Total	(1,597,000)	(2,953,000)	(4,411,000)
Federal, Total	24,935,000	20,339,000	(460,000)
State, Total	6,196,000	3,321,000	(1,247,000)
Foreign, Total	(598,000)	(1,538,000)
Total	30,533,000	22,122,000	(1,707,000)
U.S. Federal corporate income tax rate (in hundredths)	35.00%	35.00%	35.00%
Income tax expense (benefit), reconciliation [Abstract]
Computed "expected" tax expense	29,013,000	20,125,000	14,457,000
Change in income taxes resulting from [Abstract]
State income taxes, net of federal income tax	4,027,000	2,159,000	2,217,000
Foreign income tax expense (benefit)	622,000	1,468,000	0
Deduction for domestic production activities	(1,361,000)	(1,277,000)	0
R&D tax credits	(1,652,000)	(508,000)
Other, net	(116,000)	155,000	(876,000)
Valuation allowance change	0	0	(17,505,000)
Income tax expense (benefit)	30,533,000	22,122,000	(1,707,000)
Geographical allocation of entity's income before income taxes [Abstract]
Pre-tax income from U.S. operations	86,382,000	66,087,000	41,306,000
Pre-tax loss from foreign operations	(3,487,000)	(8,587,000)	0
Total pre-tax income	82,895,000	57,500,000	41,306,000
Deferred tax liabilities [Abstract]
Percentage of valuation allowance against deferred tax assets (in hundredths)			100.00%
Unrecognized tax benefits [Roll Forward]
Balance	1,485,000	0
Additions relating to current year	589,000	1,265,000
Additions relating to prior years		220,000
Terminations of exposures relating to prior years	(1,229,000)
Balance	845,000	1,485,000	0
Amount of unrecognized tax positions that will impact effective tax rate	845,000
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
NOL carry-forward	4,400,000
Federal Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
NOL carry-forward	7,900,000
Federal Tax Authority [Member] | Research and Experimentation Tax Credit Carryforward [Member]
R&D Tax Credit Carryforward [Line Items]
R&D tax credit carryforward	600,000
Federal Tax Authority [Member] | Research and Experimentation Tax Credit Carryforward [Member] | 2003 through 2010 [Member]
R&D Tax Credit Carryforward [Line Items]
R&D tax credit carryforward	800,000
State and Local Jurisdiction [Member] | Illinois [Member]
Operating Loss Carryforwards [Line Items]
NOL carry-forward	2,200,000
Current [Member]
Deferred tax assets [Abstract]
Net operating loss carry-forward	439,000	0
Stock-based compensation	0	0
Reserve for product returns	3,189,000	2,787,000
Inventory valuation reserve	2,193,000	3,980,000
Other	3,325,000	2,974,000
Total deferred tax assets	9,146,000	9,741,000
Deferred tax liabilities [Abstract]
Prepaid expenses	(1,120,000)	(551,000)
Unamortized discount - convertible notes	0	0
Depreciation & amortization - tax over book	0	0
Other	(81,000)	0
Total deferred tax liabilities	(1,201,000)	(551,000)
Net deferred income tax asset (liability)	7,945,000	9,190,000
Noncurrent [Member]
Deferred tax assets [Abstract]
Net operating loss carry-forward	14,061,000	4,328,000
Stock-based compensation	6,630,000	4,912,000
Reserve for product returns	0	0
Inventory valuation reserve	0	0
Other	1,751,000	1,349,000
Total deferred tax assets	22,442,000	10,589,000
Deferred tax liabilities [Abstract]
Prepaid expenses	0	0
Unamortized discount - convertible notes	(4,223,000)	(5,815,000)
Depreciation & amortization - tax over book	(16,576,000)	(5,835,000)
Other	0	0
Total deferred tax liabilities	(20,799,000)	(11,650,000)
Net deferred income tax asset (liability)	$ 1,643,000	$ (1,061,000)