Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 08, 2017	Feb. 05, 2015
Stockholders Equity Note [Line Items]
Common stock authorized to be repurchased, number of shares				15,000,000.0	15,000,000.0
Common stock repurchased, shares	5,000,000
Common stock repurchased, value	$ 243,706		$ 66,057
Common stock dividends, paid per share	$ 0.16	$ 0.15	$ 0.12
Common stock dividends, total cash paid	$ 88,123	$ 82,605	$ 65,920
Payments of Ordinary Dividends, Common Stock	$ 88,123	82,605	$ 65,920
Common Stock and Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Common stock repurchased, shares	4,986,000		2,132,000
Common stock repurchased, value	$ 136,891		$ 24,222
Retained Earnings
Stockholders Equity Note [Line Items]
Common stock repurchased, value	106,815		41,835
Common stock dividends, total cash paid	$ 88,123	$ 82,605	$ 65,920