Shareholders' Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 08, 2017	Feb. 05, 2015	Feb. 05, 2013
Stockholders Equity Note [Line Items]
Common stock authorized to be repurchased, number of shares				15,000,000.0	15,000,000.0	25,000,000
Common stock repurchased, value	$ 66,057,000	$ 123,193,000.000	$ 139,238,000
Common stock dividends, paid per share	$ 0.12	$ 0.11	$ 0.10
Common stock dividends, total cash paid	$ 65,920,000	$ 61,399,000	$ 56,513,000
Payments of Ordinary Dividends, Common Stock	$ 65,920,000	$ 61,399,000	$ 56,513,000
Common Stock and Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Common stock repurchased, shares	2,132,000	4,169,000	4,243,000
Common stock repurchased, value	$ 24,222,000	$ 44,387,000	$ 122,851,000
Retained Earnings
Stockholders Equity Note [Line Items]
Common stock repurchased, value	41,835,000	78,806,000	16,387,000
Common stock dividends, total cash paid	$ 65,920,000	$ 61,399,000	$ 56,513,000