Income taxes (Reconciliation of the Differences Due to Federal Statutory Rate) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Expected federal income tax provision/credit at statutory rates									$ (9,569)	$ (11,582)	$ (1,370)
State income taxes, net of federal effect									(1,293)	(1,456)	(179)
Effect of nontaxable income, net									779	643	489
Reversal of valuation allowance									15	4	0
Tax affected disallowed merger costs									(369)	0	(974)
Rate change for deferred taxes									195	(353)	1,687
Other, net									(326)	231	169
(Provision) for income taxes	$ (4,168)	$ (2,415)	$ (2,828)	$ (1,157)	$ (3,878)	$ (2,626)	$ (2,861)	$ (3,148)	$ (10,568)	$ (12,513)	$ (178)