Loans and Allowance for Probable Loan Losses - Nonperforming Assets by Asset Class (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Nonperforming Assets by Asset Class [Abstract]
Nonaccrual loans	$ 20,321	[1]	$ 4,096	[1]
Accruing loans past due more than 90 days	1	[1]	4	[1]
Restructured loans	5,782	[1]	5,874	[1]
Other real estate owned	985		1,738
Repossessed assets	173		565
Total nonperforming assets	$ 27,262		$ 12,277

[1] Excludes PCI loans measured at fair value at acquisition.