Investment Securities (Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	$ 659,921	$ 432,752
Less than 12 months, gross unrealized losses	(11,569)	(3,944)
12 months or longer, fair value	229,118	243,044
12 months or longer, gross unrealized losses	(9,076)	(6,172)
Total, fair value	889,039	675,796
Total, gross unrealized losses	(20,645)	(10,116)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	5,000	12,006
Less than 12 months, gross unrealized losses	(7)	(8)
12 months or longer, fair value	1,999	6,999
12 months or longer, gross unrealized losses	(1)	(1)
Total, fair value	6,999	19,005
Total, gross unrealized losses	(8)	(9)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	646,962	420,746
Less than 12 months, gross unrealized losses	(11,513)	(3,936)
12 months or longer, fair value	227,119	235,056
12 months or longer, gross unrealized losses	(9,075)	(6,159)
Total, fair value	874,081	655,802
Total, gross unrealized losses	(20,588)	(10,095)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	7,959	0
Less than 12 months, gross unrealized losses	(49)	0
12 months or longer, fair value	0	989
12 months or longer, gross unrealized losses	0	(12)
Total, fair value	7,959	989
Total, gross unrealized losses	$ (49)	$ (12)