Securities Available for Sale and Held to Maturity - Gains and Losses as a Result of Calls and Disposition of Securities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gain Loss On Investments [Abstract]
Proceeds from calls and sales of securities	$ 0	$ 26,409	$ 0	$ 26,409
Gross realized gains	0	1	0	1
Gross realized (losses)	$ 0	$ 0	$ 0	$ 0

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration