FHLB and other borrowings (Details) - Schedule of components of FHLB and other borrowings and weighted average interest rates (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
By type of borrowing:
FHLB and other borrowings	$ 525,148	$ 495,553
Weighted average interest rates	1.51%	1.48%
By remaining period to maturity:
One year or less	238,148	258,553
One year or less	0.50%	0.50%
One to two years	55,000	30,000
One to two years	1.20%	1.40%
Two to three years	71,000	71,000
Two to three years	2.33%	2.33%
Three to four years	96,000	96,000
Three to four years	2.67%	2.67%
Four to five years	25,000
Four to five years	1.85%
Greater than five years	40,000	40,000
Greater than five years	3.43%	3.42%
Federal Home Loan Bank Advances [Member]
By type of borrowing:
FHLB and other borrowings	494,148	464,553
Weighted average interest rates	1.23%	1.18%
Repurchase Agreements [Member]
By type of borrowing:
FHLB and other borrowings	$ 31,000	$ 31,000
Weighted average interest rates	5.90%	5.90%