Loans and the Allowance for Loan Losses (Details 8) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Sep. 01, 2013
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	$ 344,425		$ 448,930		$ 899,236
Impaired Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	8,004		24,519
Other Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	135,037		157,155
Not Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	201,384		267,256
Contractually-required principal and interest
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	477,438		623,425		1,112,979
Contractually-required principal and interest | Impaired Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	32,451		67,976
Contractually-required principal and interest | Other Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	163,271		201,215
Contractually-required principal and interest | Not Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	281,716		354,234
Nonaccretable difference
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(100,580)	[1]	(134,545)	[1]	70,334	[1]
Nonaccretable difference | Impaired Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(24,446)	[1]	(43,456)	[1]
Nonaccretable difference | Other Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(25,611)	[1]	(40,301)	[1]
Nonaccretable difference | Not Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(50,523)	[1]	(50,788)	[1]
Cash flows expected to be collected
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	376,858		488,880		1,042,645
Cash flows expected to be collected | Impaired Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	8,005		24,520
Cash flows expected to be collected | Other Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	137,660		160,914
Cash flows expected to be collected | Not Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	231,193		303,446
Accretable yield
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(32,433)	[2]	(39,950)	[2]	143,409	[2]
Accretable yield | Impaired Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(1)	[2]	(1)	[2]
Accretable yield | Other Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	(2,623)	[2]	(3,759)	[2]
Accretable yield | Not Covered Loans
Fair value of loans determined to be impaired and not to be impaired at the time of acquisition
Loans acquired with deteriorated credit quality	$ (29,809)	[2]	$ (36,190)	[2]

[1] Represents contractual principal cash flows of $95,081 and $125,086, respectively, and interest cash flows of $5,499 and $9,459, respectively, not expected to be collected.

[2] Represents contractual interest payments expected to be collected of $2,798 and $3,936, respectively, and purchase discount of $29,635 and $36,014, respectively.