Business Combinations - Pro Forma Financial Information (Details) - DNB - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total Revenue		$ 341,117	$ 325,668
Net Income	[1]	$ 120,964	$ 116,046
Basic (in usd per share)	[1]	$ 3.03	$ 2.90
Diluted (in usd per share)	[1]	$ 3.03	$ 2.88
Merger-related expenses		$ 13,600

[1] Excludes non-recurring merger-related expenses of $13.6 million, net of tax at 21 percent.