Securities Available-for-Sale - Gross Unrealized Losses on Mortgage-Backed Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	$ 2,757	$ 4,710
Estimated Fair value, less than 12 months	226,594	226,112
Unrealized losses, 12 months or more	4,022	5,449
Estimated Fair value, 12 months or more	101,143	106,398
Unrealized losses, total	6,779	10,159
Estimated fair value, total	327,737	332,510
Equity investments-mutual funds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months		15
Estimated Fair value, less than 12 months		947
Unrealized losses, 12 months or more		0
Estimated Fair value, 12 months or more		0
Unrealized losses, total		15
Estimated fair value, total		947
Pass-through Certificates | GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	1,567	2,703
Estimated Fair value, less than 12 months	84,923	121,878
Unrealized losses, 12 months or more	189	595
Estimated Fair value, 12 months or more	11,234	8,402
Unrealized losses, total	1,756	3,298
Estimated fair value, total	96,157	130,280
Real estate mortgage investment conduits (REMICs) | GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	1,124	1,622
Estimated Fair value, less than 12 months	104,018	75,586
Unrealized losses, 12 months or more	3,832	4,844
Estimated Fair value, 12 months or more	89,828	97,726
Unrealized losses, total	4,956	6,466
Estimated fair value, total	193,846	173,312
Real estate mortgage investment conduits (REMICs) | Non-GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	0	0
Estimated Fair value, less than 12 months	0	0
Unrealized losses, 12 months or more	1	10
Estimated Fair value, 12 months or more	81	270
Unrealized losses, total	1	10
Estimated fair value, total	81	270
Debt securities | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months		6
Estimated Fair value, less than 12 months		1,679
Unrealized losses, 12 months or more		0
Estimated Fair value, 12 months or more		0
Unrealized losses, total		6
Estimated fair value, total		1,679
Debt securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	66	364
Estimated Fair value, less than 12 months	37,653	26,022
Unrealized losses, 12 months or more	0	0
Estimated Fair value, 12 months or more	0	0
Unrealized losses, total	66	364
Estimated fair value, total	$ 37,653	$ 26,022