Investment Securities (Continuous Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014 securities	Dec. 31, 2013 securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	$ 1,154	$ 232,060
Less than 12 months, gross unrealized losses	4	17,408
12 months or more, estimated fair value	277,630	97,940
12 months or more, gross unrealized losses	6,162	9,083
Total, estimated fair value	278,784	330,000
Total, gross unrealized losses	6,166	26,491
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	141,125
Less than 12 months, gross unrealized losses	0	10,670
12 months or more, estimated fair value	122,876	0
12 months or more, gross unrealized losses	1,702	0
Total, estimated fair value	122,876	141,125
Total, gross unrealized losses	1,702	10,670
Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	1,154	373,185
Less than 12 months, gross unrealized losses	4	28,078
12 months or more, estimated fair value	400,506	97,940
12 months or more, gross unrealized losses	7,864	9,083
Total, estimated fair value	401,660	471,125
Total, gross unrealized losses	7,868	37,161
12 months or more, number of securities	33	10
Residential mortgage-backed securities - GSE [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	222,475
Less than 12 months, gross unrealized losses	0	16,585
12 months or more, estimated fair value	245,457	76,501
12 months or more, gross unrealized losses	5,593	7,755
Total, estimated fair value	245,457	298,976
Total, gross unrealized losses	5,593	24,340
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	131,817
Less than 12 months, gross unrealized losses	0	9,907
12 months or more, estimated fair value	112,878	0
12 months or more, gross unrealized losses	1,635	0
Total, estimated fair value	112,878	131,817
Total, gross unrealized losses	1,635	9,907
Residential mortgage-backed securities - Private [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	1,154
Less than 12 months, gross unrealized losses	4
12 months or more, estimated fair value	0
12 months or more, gross unrealized losses	0
Total, estimated fair value	1,154
Total, gross unrealized losses	4
Commercial mortgage-backed securities - GSE [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	0
Less than 12 months, gross unrealized losses	0	0
12 months or more, estimated fair value	21,958	21,439
12 months or more, gross unrealized losses	419	1,328
Total, estimated fair value	21,958	21,439
Total, gross unrealized losses	419	1,328
Commercial mortgage-backed securities - Private [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	9,585
Less than 12 months, gross unrealized losses	0	823
12 months or more, estimated fair value	10,215	0
12 months or more, gross unrealized losses	150	0
Total, estimated fair value	10,215	9,585
Total, gross unrealized losses	150	823
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, estimated fair value	0	9,308
Less than 12 months, gross unrealized losses	0	763
12 months or more, estimated fair value	9,998	0
12 months or more, gross unrealized losses	67	0
Total, estimated fair value	9,998	9,308
Total, gross unrealized losses	$ 67	$ 763