Other Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Total intangible assets	$ 29,981	$ 34,271
Core deposit intangible assets
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Gross original amount	56,456	59,143
Accumulated amortization	26,475	24,884
Total intangible assets	29,981	34,259
Non-compete intangible assets
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Total intangible assets	$ 0	$ 12