Securities (Unrealized Gross Losses and Estimated Fair values of Investment Securities by Length of Time that Individual Securities in Each Category in Continuous Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	$ 511,991	$ 347,651
Unrealized Losses - Less Than 12 Months	(8,686)	(3,432)
Fair Value - 12 Months or More	103,708	192,809
Unrealized Losses - 12 Months or More	(3,850)	(6,709)
Fair Value	615,699	540,460
Unrealized Losses	(12,536)	(10,141)
Available-for-sale Securities, Amortized Cost Basis	789,229	756,186
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3,174	4,293
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	42,805	5,507
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(631)	(61)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	42,805	5,507
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(631)	(61)
Obligations of U.S. government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	348,579	234,897
Unrealized Losses - Less Than 12 Months	(5,780)	(2,351)
Fair Value - 12 Months or More	29,496	45,629
Unrealized Losses - 12 Months or More	(1,335)	(1,506)
Fair Value	378,075	280,526
Unrealized Losses	(7,115)	(3,857)
Available-for-sale Securities, Amortized Cost Basis		4,971
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax		69
Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	163,412	111,143
Unrealized Losses - Less Than 12 Months	(2,906)	(1,068)
Fair Value - 12 Months or More	74,212	147,180
Unrealized Losses - 12 Months or More	(2,515)	(5,203)
Fair Value	237,624	258,323
Unrealized Losses	(5,421)	(6,271)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months		996
Unrealized Losses - Less Than 12 Months		(4)
Fair Value - 12 Months or More		0
Unrealized Losses - 12 Months or More		0
Fair Value		996
Unrealized Losses		(4)
Available-for-sale Securities, Amortized Cost Basis	5,481	1,000
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	132
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months		615
Unrealized Losses - Less Than 12 Months		(9)
Fair Value - 12 Months or More		0
Unrealized Losses - 12 Months or More		0
Fair Value		615
Unrealized Losses		(9)
Available-for-sale Securities, Amortized Cost Basis	632	712
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	109	2
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	485,222	419,429
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	2,515	3,474
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	8,848	17,355
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	153	339
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(631)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (631)
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		5,507
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(61)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		5,507
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ (61)