Income taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Components Of Income Tax Expense Benefit [Line Items]
Valuation allowance	$ 26,361,000	$ 19,124,000
Net increase in valuation allowance	7,300,000
Operating loss carry forwards, state, net of tax	21,900,000
Operating loss carry forwards, foreign, net of tax	102,700,000
Income tax expense	25,138,000	14,165,000	24,031,000
Income tax effective rate	35.80%	(690.00%)	43.70%
Income tax effective rate excluding the impact of the charges related to the U.S Government resolutions (as a percent)	42.00%	149.10%
Unrecognized tax benefit	1,200,000	600,000
Accrued interest and penalties related to unrecognized tax benefits	800,000	600,000
Unremitted foreign earnings	292,000,000	285,300,000
Total cash and cash equivalents	31,055,000	33,207,000	13,561,000	13,328,000
U.S. Subsidiary [Member]
Components Of Income Tax Expense Benefit [Line Items]
Unremitted foreign earnings	293,800,000
U.S [Member]
Components Of Income Tax Expense Benefit [Line Items]
Total cash and cash equivalents	52,300,000
Restricted cash	21,300,000
Non-Us Subsidiary [Member]
Components Of Income Tax Expense Benefit [Line Items]
Total cash and cash equivalents	$ 31,000,000