Fair Value Measurements - Financial Instruments Classified Within Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Total investment securities available for sale
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Beginning Balance	$ 0	$ 200
Ending Balance	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Mortgage derivative loss	0	0
Total investment securities available for sale | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfer of level 3 to level 2 based on new pricing information		200
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Transfer out of level 3 securities		(200)
Derivative Financial Instruments
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	1,225	3,114
Mortgage derivative loss	1,501	(1,889)
Ending Balance	$ 2,726	1,225
Derivative Financial Instruments | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfer of level 3 to level 2 based on new pricing information		0
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Transfer out of level 3 securities		$ 0
Investment security
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfer of level 3 to level 2 based on new pricing information			$ 200
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Transfer out of level 3 securities			$ (200)