Securities - Available-for-sale Securities in Continuous Loss Position (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) investment	Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 82,247	$ 67,058
Less than 12 Months, Gross Unrealized Losses	(1,799)	(475)
12 Months or Greater, Fair Value	47,110	50,580
12 Months or Greater, Gross Unrealized Losses	(1,845)	(1,312)
Total, Fair Value	129,357	117,638
Total, Gross Unrealized Losses	(3,644)	(1,787)
U.S. Government-sponsored enterprises (GSEs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	16,016	1,358
Less than 12 Months, Gross Unrealized Losses	(281)	(1)
12 Months or Greater, Fair Value	13,287	13,420
12 Months or Greater, Gross Unrealized Losses	(563)	(431)
Total, Fair Value	29,303	14,778
Total, Gross Unrealized Losses	$ (844)	(432)
Number of investments in unrealized loss positions | investment	9
Municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 5,915	3,418
Less than 12 Months, Gross Unrealized Losses	(129)	(43)
12 Months or Greater, Fair Value	2,077	2,112
12 Months or Greater, Gross Unrealized Losses	(136)	(104)
Total, Fair Value	7,992	5,530
Total, Gross Unrealized Losses	$ (265)	(147)
Number of investments in unrealized loss positions | investment	19
Other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 0	950
Less than 12 Months, Gross Unrealized Losses	0	(24)
12 Months or Greater, Fair Value	924	0
12 Months or Greater, Gross Unrealized Losses	(51)	0
Total, Fair Value	924	950
Total, Gross Unrealized Losses	$ (51)	(24)
Number of investments in unrealized loss positions | investment	1
Mortgage-backed securities (GSEs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 60,316	61,332
Less than 12 Months, Gross Unrealized Losses	(1,389)	(407)
12 Months or Greater, Fair Value	30,822	35,048
12 Months or Greater, Gross Unrealized Losses	(1,095)	(777)
Total, Fair Value	91,138	96,380
Total, Gross Unrealized Losses	$ (2,484)	$ (1,184)
Number of investments in unrealized loss positions | investment	63