Employee Benefit Plans - Profit Sharing Plan (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Profit sharing expense		$ 43,104	$ 41,886	$ 33,309
Profit Sharing Expense
Defined Contribution Plan Disclosure [Line Items]
Profit sharing expense	[1]	7,803	7,346	6,171
Company dividends received by the Profit Sharing Plan		$ 457	$ 441	$ 494
Company shares held by the Profit Sharing Plan at the end of the year:
Number of shares		1,047,213	1,079,975	1,175,858
Fair value		$ 20,745	$ 25,930	$ 29,667

[1] Included in retirement and other employee benefits in the Consolidated Statements of Income.