Long-term debt - Additional Information (Detail)	12 Months Ended						1 Months Ended		12 Months Ended							1 Months Ended			12 Months Ended			12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 EUR (€)	Dec. 31, 2011 EUR (€)	Dec. 31, 2012 LIBOR [Member]	May 31, 2012 Revolving Credit Facility [Member] USD ($)	Aug. 31, 2010 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] USD ($)	Sep. 30, 2012 Revolving Credit Facility [Member] USD ($)	Jun. 30, 2012 Revolving Credit Facility [Member] USD ($)	Dec. 31, 2011 Revolving Credit Facility [Member] USD ($)	Aug. 30, 2010 Revolving Credit Facility [Member] USD ($)	Dec. 31, 2011 Revolving Credit Facility [Member] LIBOR [Member] USD ($)	Dec. 31, 2011 Revolving Credit Facility [Member] Base rate [Member] USD ($)	May 31, 2012 Term Loan Facility [Member] USD ($)	May 31, 2011 Term Loan Facility [Member] USD ($)	Aug. 31, 2010 Term Loan Facility [Member] USD ($)	Dec. 31, 2011 Term Loan Facility [Member] USD ($)	Dec. 31, 2012 Term Loan Facility [Member] USD ($)	Dec. 31, 2011 Term Loan Facility [Member] LIBOR [Member] USD ($)	Dec. 31, 2012 Term Loan Facility [Member] Base rate [Member] Maximum [Member]	Aug. 31, 2010 New Credit Agreement [Member] USD ($)	Dec. 31, 2011 New Credit Agreement [Member] LIBOR [Member] Maximum [Member]	Dec. 31, 2011 New Credit Agreement [Member] Base rate [Member] Maximum [Member]	Dec. 31, 2012 Prior Credit Agreement [Member]	Dec. 31, 2011 Prior Credit Agreement [Member]
Debt Instrument [Line Items]
Debt instrument term (in years)								5 years										5 years
Maximum borrowing capacity	$ 7,600,000	$ 8,100,000		€ 5,800,000	€ 6,300,000								$ 200,000,000
Maximum borrowing capacity																		100,000,000
Maximum additional borrowing capacity available																							50,000,000
Repayment of debt obligation	188,695,000	7,500,000	36,269,000													87,500,000
Repayment of debt obligation							57,500,000		20,000,000
Amount outstanding	100,000	1,300,000								20,000,000	20,000,000	117,400,000							91,300,000
Margin on variable rate						2.50%								3.00%	2.00%						3.00%			3.25%	2.25%
Variable rate basis																						LIBOR
Portion of credit facility charged at variable rate														100,000,000	17,400,000						100,000,000
Effective interest rate (as a Percent)																										2.70%	3.40%
Amount of restricted net assets	213,400,000	162,700,000
Restricted cash	21,314,000	45,476,000
Debt issuance costs incurred																	800,000		5,000,000
Deferred debt issuance costs, net																			$ 3,500,000	$ 1,800,000