Securities - Available-for-sale Securities in Continuous Loss Position (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) investment	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 41,276	$ 88,133
Less than 12 Months, Gross Unrealized Losses	(341)	(1,433)
12 Months or Greater, Fair Value	25,990	8,948
12 Months or Greater, Gross Unrealized Losses	(539)	(400)
Total, Fair Value	67,266	97,081
Total, Gross Unrealized Losses	(880)	(1,833)
U.S. Government-sponsored enterprises (GSEs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	6,110	14,702
Less than 12 Months, Gross Unrealized Losses	(113)	(564)
12 Months or Greater, Fair Value	7,804	0
12 Months or Greater, Gross Unrealized Losses	(196)	0
Total, Fair Value	13,914	14,702
Total, Gross Unrealized Losses	$ (309)	(564)
Number of investments in unrealized loss positions | investment	5
Municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 1,839	6,368
Less than 12 Months, Gross Unrealized Losses	(18)	(179)
12 Months or Greater, Fair Value	1,305	0
12 Months or Greater, Gross Unrealized Losses	(23)	0
Total, Fair Value	3,144	6,368
Total, Gross Unrealized Losses	$ (41)	(179)
Number of investments in unrealized loss positions | investment	8
Other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 938
Less than 12 Months, Gross Unrealized Losses	(35)
12 Months or Greater, Fair Value	0
12 Months or Greater, Gross Unrealized Losses	0
Total, Fair Value	938
Total, Gross Unrealized Losses	$ (35)
Number of investments in unrealized loss positions | investment	1
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 32,389	67,063
Less than 12 Months, Gross Unrealized Losses	(175)	(690)
12 Months or Greater, Fair Value	16,881	8,948
12 Months or Greater, Gross Unrealized Losses	(320)	(400)
Total, Fair Value	49,270	76,011
Total, Gross Unrealized Losses	$ (495)	$ (1,090)
Number of investments in unrealized loss positions | investment	40