Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Item Effected
Assets	$ 5,887,284	$ 5,486,268
Liabilities and shareholers' equity	5,887,284	$ 5,486,268
Minimum | Accounting Standards Update 2016-02
Item Effected
Assets	7,000
Liabilities and shareholers' equity	7,000
Maximum | Accounting Standards Update 2016-02
Item Effected
Assets	10,000
Liabilities and shareholers' equity	$ 10,000