Share-Based Compensation - Summary of Information Of SERP (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
SERP expense	$ 5,900	$ 5,985	$ 4,252
SERP
Defined Benefit Plan Disclosure [Line Items]
SERP expense	$ 547	$ 503	$ 511
Treasury shares issued to fund SERP expense (in shares)	14	9	13
SERP trust account balance at December 31	$ 39,766	$ 42,467	$ 34,599
Unrealized gain (loss) recorded in SERP liability account	$ (1,469)	$ 4,534	$ 1,495