Acquired Loans - Changes in Accretable Yield of Acquired Loans (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Change in accretable difference on acquired loans [Abstract]
Accretable yield at beginning of period		$ (52,672)	$ (77,149)	$ (77,149)
Accretion to interest income		5,230	10,197
Disposals		1,067	3,103
Reclassification to / (from) nonaccretable difference	[1]	(3,403)	(6,179)
Accretable yield at end of period		$ (49,778)	$ (70,028)	$ (52,672)

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