Property, plant and equipment, net (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment	[1]	$ 186,287	$ 186,331
Less: Accumulated depreciation	[2]	(110,275)	(103,865)
Total amount of property, plant and equipment, net	[3]	76,012	82,466
Land Use Rights and Buildings [Member]
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment		52,538	48,956
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment		116,759	119,597
Electronic Equipment [Member]
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment		7,693	7,706
Motor Vechicles [Member]
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment		4,686	4,609
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total amount of property, plant and equipment		$ 4,611	$ 5,463

[1] Through the acquisition of Fujian Qiaolong in the second quarter of 2014, the Company acquired $3.7 million of property, plant and equipment, consisting of $3.4 million of land use rights and buildings, $0.2 million of machinery and equipment, and $0.1 million of motor vehicles, which are depreciated over a weighted average life of 43.0 years, 3.5 years, and 3.1 years, respectively.

[2] Depreciation charges were $3.4 million and $3.7 million for the three months ended September 30, 2015 and 2014, respectively, and $11.0 million and $11.4 million for the nine months ended September 30, 2015 and 2014, respectively.

[3] As of September 30, 2015 and December 31, 2014, the Company had pledged property, plant and equipment with net book value of $41.0 million and $45.5 million, respectively, for its comprehensive credit facilities with banks in China.