Securities (Fair value and gross unrealized losses) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities
Less than 12 months, fair value	$ 137,735	$ 461,003
Less than 12 months, unrealized (losses)	(1,204)	(21,912)
12 months or more, fair value	276,200	37,423
12 months or more, unrealized (losses)	(15,920)	(4,637)
Total, fair value	413,935	498,426
Total, unrealized (losses)	(17,124)	(26,549)
Held-to-maturity Securities
Less than 12 months, fair value	95,466	211,326
Less than 12 months, unrealized (losses)	(679)	(18,293)
12 months or more, fair value	176,613	22,579
12 months or more, unrealized (losses)	(10,415)	(2,421)
Total, fair value	272,079	233,905
Total, unrealized (losses)	(11,094)	(20,714)
U.S. Government agency securities [Member]
Held-to-maturity Securities
Less than 12 months, fair value	0	110,435
Less than 12 months, unrealized (losses)	0	(13,661)
12 months or more, fair value	141,020	22,579
12 months or more, unrealized (losses)	(8,089)	(2,421)
Total, fair value	141,020	133,014
Total, unrealized (losses)	(8,089)	(16,082)
Residential mortgage-backed securities [Member]
Held-to-maturity Securities
Less than 12 months, fair value	6,926
Less than 12 months, unrealized (losses)	(45)
12 months or more, fair value	0
12 months or more, unrealized (losses)	0
Total, fair value	6,926
Total, unrealized (losses)	(45)
Agency CMOs [Member]
Held-to-maturity Securities
Less than 12 months, fair value	87,527	98,082
Less than 12 months, unrealized (losses)	(631)	(4,465)
12 months or more, fair value	34,961	0
12 months or more, unrealized (losses)	(2,318)	0
Total, fair value	122,488	98,082
Total, unrealized (losses)	(2,949)	(4,465)
Municipal securities [Member]
Held-to-maturity Securities
Less than 12 months, fair value	1,013	2,809
Less than 12 months, unrealized (losses)	(3)	(167)
12 months or more, fair value	632	0
12 months or more, unrealized (losses)	(8)	0
Total, fair value	1,645	2,809
Total, unrealized (losses)	(11)	(167)
U.S. Government agency securities [Member]
Available-for-sale Securities
Less than 12 months, fair value	0	8,077
Less than 12 months, unrealized (losses)	0	(918)
12 months or more, fair value	31,827	21,849
12 months or more, unrealized (losses)	(2,168)	(3,151)
Total, fair value	31,827	29,926
Total, unrealized (losses)	(2,168)	(4,069)
Residential mortgage-backed securities [Member]
Available-for-sale Securities
Less than 12 months, fair value	26,051	62,500
Less than 12 months, unrealized (losses)	(19)	(3,295)
12 months or more, fair value	31,547	0
12 months or more, unrealized (losses)	(1,090)	0
Total, fair value	57,598	62,500
Total, unrealized (losses)	(1,109)	(3,295)
Agency CMOs [Member]
Available-for-sale Securities
Less than 12 months, fair value	110,667	363,993
Less than 12 months, unrealized (losses)	(1,181)	(16,182)
12 months or more, fair value	204,489	15,574
12 months or more, unrealized (losses)	(12,347)	(1,486)
Total, fair value	315,156	379,567
Total, unrealized (losses)	(13,528)	(17,668)
Municipal securities [Member]
Available-for-sale Securities
Less than 12 months, fair value	1,017	26,433
Less than 12 months, unrealized (losses)	(4)	(1,517)
12 months or more, fair value	8,337	0
12 months or more, unrealized (losses)	(315)	0
Total, fair value	9,354	26,433
Total, unrealized (losses)	$ (319)	$ (1,517)