Acquired Loans - Changes in the Carrying Value of Acquired Loans (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Carrying value of acquired loans [Abstract]
Accretion to interest income		$ 5,230	$ 10,197
Noncovered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		361,452
Carrying value, net, ending		336,569		$ 361,452
Covered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		16,967
Carrying value, net, ending		14,651		16,967
Acquired Not ASC 310-30 [Member] | Noncovered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning	[1]	66,086	81,091	81,091
Accretion to interest income	[1]	2		479
Payments received, net	[1]	(5,700)		(15,484)
Other	[1],[2]	0		0
Less change in allowance for loan losses, acquired loans	[1]	(1)		0
Carrying value, net, ending	[1]	60,387		66,086
Acquired Not ASC 310-30 [Member] | Covered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning	[1]	1,571	1,604	1,604
Accretion to interest income	[1]	1		0
Payments received, net	[1]	(60)		(33)
Other	[1],[2]	0		0
Less change in allowance for loan losses, acquired loans	[1]	0		0
Carrying value, net, ending	[1]	1,512		1,571
Acquired Impaired [Member] | Noncovered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		295,366	434,151	434,151
Accretion to interest income		4,821		28,193
Payments received, net		(22,169)		(164,671)
Other	[2]	116		(1,589)
Less change in allowance for loan losses, acquired loans		(1,952)		(718)
Carrying value, net, ending		276,182		295,366
Acquired Impaired [Member] | Covered Loans [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		15,396	$ 20,504	20,504
Accretion to interest income		409		2,308
Payments received, net		(2,683)		(8,592)
Other	[2]	(393)		391
Less change in allowance for loan losses, acquired loans		410		785
Carrying value, net, ending		$ 13,139		$ 15,396

[1] "Acquired Not ASC 310-30" loans consist of revolving credit agreements and commercial leases that are not in scope for FASB ASC Topic 310-30, "Loans and Debt Securities Acquired with Deteriorated Credit Quality."

[2] Includes miscellaneous timing adjustments as well as acquired loan terminations through foreclosure, charge-off and other terminations.