Acquired Loans - Changes in Accretable Yield of Acquired Loans (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in accretable difference on acquired loans [Abstract]
Accretable yield at beginning of period		$ (38,918)	$ (52,672)	$ (77,149)
Additions due to acquisition	[1]	(784)
Accretion to interest income		14,924	18,405	30,501
Disposals		2,868	6,488	10,013
Reclassification from nonaccretable difference	[2]	(9,516)	(11,139)	(16,037)
Accretable yield at end of period		$ (31,426)	$ (38,918)	$ (52,672)

[1] Accretable yield on loans acquired from Reliance on April 7, 2017

[2] Reclassifications from nonaccretable difference are due to lower loss expectations and improvements in expected cash flows.