Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	May 07, 2018	Mar. 31, 2018	Mar. 23, 2018	May 09, 2016	Aug. 05, 2015	Dec. 31, 2017	Jun. 30, 2016
Class of Stock [Line Items]
Liquidation preference value				$ 137,500
Carrying Amount		$ 132,097				$ 132,097
Number of shares authorized to be repurchased							950,000
Shares authorized to be repurchased		747,494
Series B Preferred Stock
Class of Stock [Line Items]
Ownership per share					6.625%
Liquidation preference value					$ 80,000
Carrying Amount		$ 76,812				76,812
Series C Preferred Stock
Class of Stock [Line Items]
Ownership per share				6.60%
Liquidation preference value				$ 57,500
Carrying Amount		55,285				$ 55,285
Gibraltar Private Bank & Trust Company
Class of Stock [Line Items]
Cash consideration		$ 214,700	$ 7
Gibraltar Private Bank & Trust Company | Common Stock
Class of Stock [Line Items]
Common stock issued (shares)			2,787,773
Common stock issued			$ 214,659
Common stock issued (in dollars per share)			$ 77.00
Number of shares issued per share acquired			$ 1.9749
Subsequent Event
Class of Stock [Line Items]
Treasury stock acquired (shares)	180,000
Treasury stock acquired	$ 13,700