Goodwill and Other Intangible Assets - Changes in carrying amounts of goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	$ 526,181	$ 447,615
Accumulated Impairment Losses, beginning balance	(305,590)	(305,590)
Goodwill, net of Accumulated Impairment Losses, beginning balance	220,591	142,025
Acquisition of FOFN		54,703
Acquisition of HCSB		23,863
Acquisition of NLFC	87,379
Measurement period adjustments	(858)
Goodwill, gross, ending balance	612,702	526,181
Accumulated Impairment Losses, ending balance	(305,590)	(305,590)
Goodwill, net of Accumulated Impairment Losses, ending balance	$ 307,112	$ 220,591