Shareholders' Equity - Share Repurchases (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Shareholders Equity [Abstract]
Total number of shares repurchased and retired	3,184	1,028	2,908
Total investment	$ 348,663	$ 90,461	$ 245,816

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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Balance Type:	debit
Period Type:	duration