Income taxes (Details) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Current      
Federal $ (878,000) $ 11,481,000 $ (3,795,000)
State (173,000) (1,045,000) (1,110,000)
International 300,000 103,000 74,000
Total current (751,000) 10,539,000 (4,831,000)
Deferred      
Federal 12,679,000 3,758,000 19,055,000
State 1,028,000 (375,000) 1,606,000
International 152,000 0 0
Total deferred 13,859,000 3,383,000 20,661,000
Total provision for income taxes 13,108,000 13,922,000 15,830,000
Net deferred tax asset [Abstract]      
Net operating loss carryforward 23,256,000 26,102,000  
Research and development carryforward 7,395,000 3,556,000  
Stock compensation 6,378,000 5,289,000  
Foreign deferrals 64,090,000 64,009,000  
Deferred revenue 0 0  
Other 4,522,000 9,005,000  
Deferred tax asset 105,641,000 107,961,000  
Fixed assets (32,588,000) (22,040,000)  
Other (5,714,000) (6,158,000)  
Deferred tax liability (38,302,000) (28,198,000)  
Valuation allowance (68,846,000) (67,412,000)  
Net deferred tax asset (1,507,000) 12,351,000  
Income tax reconciliation [Abstract]      
US 52,749,000 52,391,000 66,756,000
International (8,506,000) (14,945,000) (27,907,000)
Earnings before taxes on income 44,243,000 37,446,000 38,849,000
Federal tax at statutory rates 15,485,000 13,106,000 13,597,000
State taxes, net of federal benefit 538,000 (2,079,000) 46,000
Impact of foreign operations (1,116,000) (3,604,000) (2,371,000)
Change in valuation allowance 1,434,000 4,629,000 3,193,000
Effect of foreign rates 0 (22,000) (12,000)
Tax credits (5,918,000) (2,904,000) (1,405,000)
Other differences (227,000) 139,000 556,000
Permanent differences 2,912,000 4,657,000 2,226,000
Total provision for income taxes 13,108,000 13,922,000 15,830,000
Effective annual tax rate (in hundredths) 30.00% 37.00% 41.00%
Research and Development Tax Credit [Member]
      
Tax Credit Carryforward [Line Items]      
Tax credit carryforward, amount 7,400,000    
Tax credit carryforwards, expiration date Dec. 31, 2023    
U.S. Federal Tax Authority [Member]
      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 34,100,000    
Operating loss carryforwards, expiration year Dec. 31, 2026    
State and Local Jurisdiction [Member]
      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 211,500,000    
Operating loss carryforwards, expiration year Dec. 31, 2018    
Foreign Tax Authority [Member]
      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards $ 227,600,000    
Period of change in the nature or conduct of business following change in ownership 3 years