Income taxes (Reconciliation of the Differences Due to Federal Statutory Rate) (Details) (USD $)
In Thousands, unless otherwise specified
0 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Tax Disclosure [Abstract]        
Expected federal income tax credit at statutory rates   $ (1,370) $ (238) $ (2,050)
State income taxes, net of federal effect   (179) (33) (263)
Effect of nontaxable income, net   489 547 583
Valuation allowance for deferred tax assets   0 0 10,762
Reversal of valuation allowance (41,600) 0 41,632 0
Section 382 impairment re-evaluation   0 8,163 (8,163)
Tax affected disallowed merger costs   (974) 0 0
Rate change for deferred taxes   1,687 52 (814)
Other, net   169 23 (134)
Benefit (provision) for income taxes   $ (178) $ 50,146 $ (79)