Business Combinations - (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Business Combinations
Combined business value after business combination	$ 3,100,000,000	$ 3,100,000,000
Business combination one time pre-tax severance, retention, acquisition and integration costs	8,214,000	8,829,000
Acquisition and integration related costs	$ 4,821,000	$ 5,436,000

Costs incurred to effect a business combination which have been expensed during the period. Such costs could include business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

No definition available.

Name:	us-gaap_BusinessCombinationIntegrationRelatedCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration