Derivatives - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) derivative	Jun. 30, 2017 USD ($) derivative	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Notional Amount	$ 100,000
Stockholders' equity			$ 671,857	$ 596,729		$ 330,498	$ 236,674
Cash collateral pledged on derivatives			13,904
Designated as hedging:
Derivative [Line Items]
Notional Amount			30,000	$ 130,000
Subordinated Debentures
Derivative [Line Items]
Number of derivative instruments | derivative					2
Long-term debt					$ 30,930
Interest rate swaps
Derivative [Line Items]
Number of derivative instruments | derivative				3	3
Interest rate swaps | Designated as hedging:
Derivative [Line Items]
Notional Amount			30,000	$ 130,000
Fair value of interest rate swap				1,127
Interest rate swaps | Subordinated Debentures
Derivative [Line Items]
Notional Amount					$ 30,000
Fair value of interest rate swap			721	305
Interest Rate Swaps Three
Derivative [Line Items]
Notional Amount	$ 30,000			30,000
Derivative notional amount maturity period	3 years
Interest Rate Swaps Four
Derivative [Line Items]
Notional Amount	$ 35,000			35,000
Derivative notional amount maturity period	4 years
Interest Rate Swaps Five
Derivative [Line Items]
Notional Amount	$ 35,000			$ 35,000
Derivative notional amount maturity period	5 years
Gain on canceled derivatives		$ 1,564
Accumulated Gain (Loss), Net, Cash Flow Hedge, Paren
Derivative [Line Items]
Stockholders' equity			$ 1,436