Investment Securities - Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 111,150	$ 120,325
Less than 12 months, unrealized losses	1,514	513
More than 12 months, fair value	103,807	124,903
More than 12 months, unrealized losses	817	869
Fair Value	214,957	245,228
Unrealized Losses	2,331	1,382
U.S. Treasury and government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	101,236	116,331
Less than 12 months, unrealized losses	1,495	496
More than 12 months, fair value	102,446	122,605
More than 12 months, unrealized losses	799	840
Fair Value	203,682	238,936
Unrealized Losses	2,294	1,336
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	4,008
Less than 12 months, unrealized losses	11
More than 12 months, fair value	0
More than 12 months, unrealized losses	0
Fair Value	4,008
Unrealized Losses	11
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	2,999
Less than 12 months, unrealized losses	1
More than 12 months, fair value	0
More than 12 months, unrealized losses	0
Fair Value	2,999
Unrealized Losses	1
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	2,907	3,994
Less than 12 months, unrealized losses	7	17
More than 12 months, fair value	1,361	2,298
More than 12 months, unrealized losses	18	29
Fair Value	4,268	6,292
Unrealized Losses	$ 25	$ 46