Securities, Available-for-sale (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	$ 907,810	$ 450,662
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	18,219	5,344
Investments with an Unrealized Loss of 12 months or longer, Fair Value	98,377	178,215
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	1,968	3,989
Total Investments with an Unrealized Loss, Fair Value	1,006,187	628,877
Total Investments with an Unrealized Loss, Unrealized Losses	20,187	9,333
US Treasury Securities [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	0	0
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	0	0
Investments with an Unrealized Loss of 12 months or longer, Fair Value	0	0
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	0	0
Total Investments with an Unrealized Loss, Fair Value	0	0
Total Investments with an Unrealized Loss, Unrealized Losses	0	0
U.S. Government Agency Securities [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	0	61,903
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	0	1,702
Investments with an Unrealized Loss of 12 months or longer, Fair Value	20,820	65,538
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	537	1,607
Total Investments with an Unrealized Loss, Fair Value	20,820	127,441
Total Investments with an Unrealized Loss, Unrealized Losses	537	3,309
Mortgage-backed Agency Securities [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	801,213	338,230
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	15,073	2,789
Investments with an Unrealized Loss of 12 months or longer, Fair Value	43,148	103,003
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	613	2,241
Total Investments with an Unrealized Loss, Fair Value	844,361	441,233
Total Investments with an Unrealized Loss, Unrealized Losses	15,686	5,030
State and Municipal Securities [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	87,277	6,509
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	3,068	38
Investments with an Unrealized Loss of 12 months or longer, Fair Value	312	6,135
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	1	134
Total Investments with an Unrealized Loss, Fair Value	87,589	12,644
Total Investments with an Unrealized Loss, Unrealized Losses	3,069	172
Asset-backed Securities [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	14,510	41,466
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	32	798
Investments with an Unrealized Loss of 12 months or longer, Fair Value	34,097	3,539
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	817	7
Total Investments with an Unrealized Loss, Fair Value	48,607	45,005
Total Investments with an Unrealized Loss, Unrealized Losses	849	805
Corporate Notes [Member]
Available-for-sale securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	4,810	2,554
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	46	17
Investments with an Unrealized Loss of 12 months or longer, Fair Value	0	0
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	0	0
Total Investments with an Unrealized Loss, Fair Value	4,810	2,554
Total Investments with an Unrealized Loss, Unrealized Losses	$ 46	$ 17