Segment reporting (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Total assets
Total	$ 1,738,419				$ 1,494,534				$ 1,738,419	$ 1,494,534
Goodwill
Total	672,086				631,077				672,086	631,077
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	278,604	283,157	267,326	272,404	247,364	242,007	231,864	258,116	1,101,491	979,351	913,866
Long-lived assets	188,357				152,733				188,357	152,733
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									198,630	159,327	189,005
Long-lived assets	159,766				130,314				159,766	130,314
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									336,689	284,932	255,874
Long-lived assets	6,459				5,434				6,459	5,434
Rest of World
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									566,172	535,092	468,987
Long-lived assets	22,132				16,985				22,132	16,985
Total segments
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,101,491	977,682	912,671
Dental CAD/CAM Systems
Total assets
Total	834,441				657,595				834,441	657,595
Goodwill
Total	315,880				296,605				315,880	296,605
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									409,328	334,539	306,743
Imaging Systems
Total assets
Total	469,373				448,360				469,373	448,360
Goodwill
Total	201,626				176,702				201,626	176,702
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									378,042	343,528	319,774
Treatment Centers
Total assets
Total	278,147				254,071				278,147	254,071
Goodwill
Total	94,092				94,662				94,092	94,662
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									210,666	197,144	183,879
Instruments
Total assets
Total	156,458				134,508				156,458	134,508
Goodwill
Total	60,488				63,108				60,488	63,108
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 103,455	$ 102,471	$ 102,275