Investment Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,057,119	$ 1,041,868
Gross unrealized gains	2,830	5,402
Gross unrealized losses	(20,645)	(10,116)
Fair value	1,039,304	1,037,154
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,007	19,014
Gross unrealized gains	0	0
Gross unrealized losses	(8)	(9)
Fair value	6,999	19,005
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,021,819	993,548
Gross unrealized gains	2,372	4,914
Gross unrealized losses	(20,588)	(10,095)
Fair value	1,003,603	988,367
State And Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,249	3,259
Gross unrealized gains	81	129
Gross unrealized losses	0	0
Fair value	3,330	3,388
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	25,044	26,047
Gross unrealized gains	377	359
Gross unrealized losses	(49)	(12)
Fair value	$ 25,372	$ 26,394