Property, plant and equipment (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Details of property, plant and equipment
Cost	$ 138,792,000	$ 119,715,000
Accumulated depreciation	(86,668,000)	(74,180,000)
Total	52,124,000	45,535,000
Depreciation expense	17,200,000	16,800,000	15,300,000
Buildings
Details of property, plant and equipment
Cost	3,829,000	3,707,000
Plant, equipment and instrumentation
Details of property, plant and equipment
Cost	125,823,000	107,379,000
Furniture and fixtures
Details of property, plant and equipment
Cost	$ 9,140,000	$ 8,629,000

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

+ References+ Details

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References+ Details

- Definition

Gross amount, at the balance sheet date, of long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

+ References+ Details

- Definition

Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

+ References+ Details