Business Combinations - purchased credit impaired loans (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Mar. 11, 2016	Dec. 31, 2015	Jul. 17, 2015
Contractually required principal and interest	$ 453,686		$ 332,458
Bank shares, Inc [Member]
Total purchased credit impaired loans acquired				$ 111,292
Bank shares, Inc [Member] | Purchased Impaired Loans [Member]
Contractually required principal and interest				12,552
Non-accretable difference				(4,249)
Cash flows expected to be collected				8,303
Accretable yield				(702)
Total purchased credit impaired loans acquired				$ 7,601
Floridian Financial Group, Inc [Member]
Total purchased credit impaired loans acquired		$ 266,137
Floridian Financial Group, Inc [Member] | Purchased Impaired Loans [Member]
Contractually required principal and interest		8,031
Non-accretable difference		(4,820)
Cash flows expected to be collected		3,211
Accretable yield		(568)
Total purchased credit impaired loans acquired		$ 2,643