Investment Securities - Investment securities with unrealized losses (Details 3) - Temporarily impaired - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value	$ 20,827	$ 330,984
Less than 12 months, Unrealized loss	163	3,659
12 months or longer, Estimated fair value	57,913	102,137
12 months or longer, Unrealized loss	1,207	2,250
Total, Estimated fair value	78,740	433,121
Total Unrealized loss	1,370	5,909
Obligations of U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value	7,849	57,409
Less than 12 months, Unrealized loss	55	388
12 months or longer, Estimated fair value	27,001	63,971
12 months or longer, Unrealized loss	152	1,045
Total, Estimated fair value	34,850	121,380
Total Unrealized loss	207	1,433
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value		21,421
Less than 12 months, Unrealized loss		235
12 months or longer, Estimated fair value	1,290	2,794
12 months or longer, Unrealized loss	17	31
Total, Estimated fair value	1,290	24,215
Total Unrealized loss	17	266
U.S. GSE's MBS-residential
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value		71,185
Less than 12 months, Unrealized loss		607
12 months or longer, Estimated fair value	5,293	11,105
12 months or longer, Unrealized loss	21	283
Total, Estimated fair value	5,293	82,290
Total Unrealized loss	21	890
U.S. GSE's MBS - commercial
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value		9,428
Less than 12 months, Unrealized loss		261
12 months or longer, Estimated fair value
12 months or longer, Unrealized loss
Total, Estimated fair value		9,428
Total Unrealized loss		261
U.S. GSE's CMO
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value	7,039	102,082
Less than 12 months, Unrealized loss	47	1,463
12 months or longer, Estimated fair value	4,334	6,584
12 months or longer, Unrealized loss	60	179
Total, Estimated fair value	11,373	108,666
Total Unrealized loss	107	1,642
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated fair value	5,939	69,459
Less than 12 months, Unrealized loss	61	705
12 months or longer, Estimated fair value	19,995	17,683
12 months or longer, Unrealized loss	957	712
Total, Estimated fair value	25,934	87,142
Total Unrealized loss	$ 1,018	$ 1,417