Deferred Compensation Benefits - Deferred Compensation Benefits Change in Benefit Obligation and Reconciliation of Fair Value (Details) - ESBP, NDBP, BDBP and FDBP [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Changes in Benefit Obligation
Benefit obligation at beginning of period	$ 29,498	$ 28,460
Service cost	343	263
Interest cost	580	553
Benefits paid	(711)	(1,066)
Acquisition	350
Actuarial loss (gain)	(821)	(1,568)
Effect of exchange rate changes	(1,642)	2,856
Benefit obligation at end of period	27,597	29,498
Reconciliation of Fair Value of Plan Assets
Fair value of plan assets at beginning of period	17,690	15,379
Actual return on plan assets	365	69
Employer contributions	1,181	1,152
Benefits paid	(1,008)	(1,052)
Effect of exchange rate changes	(825)	2,142
Fair value of plan assets at end of period	17,403	17,690
Accrued benefit cost	$ 10,194	$ 11,808