Fair value measurements (Details) {Stockholder's Equity}	9 Months Ended
	Sep. 30, 2015 USD ($)
Fair Value Measurements Using Unadjusted Quoted Market Prices (Level 1) Equity Securities
Balance	$ 21,320
Total gains or losses Included in earnings (or changes in net assets)	1,303
Purchases, issuances, sales, and settlements
Purchases	18,846
Issuances	0
Sales	(35,637)
Settlements	0
Balance	5,832
Total gains or losses Included in earnings (or changes in net assets)	8,120
Purchases, issuances, sales, and settlements
Purchases	1,061
Issuances	50,063
Sales	(1,053)
Settlements	0
Balance	64,023
Fair Value Measurements Using Quoted Prices for Identical or Similar Assets in Active Markets (Level 2) Other Investment
Balance	10,000
Total gains or losses Included in earnings (or changes in net assets)	1,410
Purchases, issuances, sales, and settlements
Sales	(1,150)
Balance	10,260
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)Equity Options
Purchases, issuances, sales, and settlements
Issuances	49,834
Balance	49,834
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Long-Term Equity Funding Agreements
Balance	55,943
Purchases, issuances, sales, and settlements
Balance	55,943
Purchases, issuances, sales, and settlements
Balance	$ 55,943