Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income from continuing operations	$ 47,006	$ 41,461	$ 92,032	$ 98,885
Income from discontinued operations, net of tax	1,208	7,440	9,695	15,149
Net income (numerator for diluted EPS)	48,214	48,901	101,727	114,034
Less: Preference stock dividend	8	10	16	19
Income attributable to common stockholders (numerator for basic EPS)	$ 48,206	$ 48,891	$ 101,711	$ 114,015
Denominator:
Weighted-average shares used in basic EPS (in shares)	187,180	186,333	187,004	186,136
Effect of dilutive shares (in shares)	934	1,044	1,053	809
Weighted-average shares used in diluted EPS (in shares)	188,114	187,377	188,057	186,945
Basic earnings per share:
Continuing operations (in dollars per share)	$ 0.25	$ 0.22	$ 0.49	$ 0.53
Discontinued operations (in dollars per share)	0.01	0.04	0.05	0.08
Net Income (in dollars per share)	0.26	0.26	0.54	0.61
Diluted earnings per share:
Continuing operations (in dollars per share)	0.25	0.22	0.49	0.53
Discontinued operations (in dollars per share)	0.01	0.04	0.05	0.08
Net Income (in dollars per share)	$ 0.26	$ 0.26	$ 0.54	$ 0.61
Anti-dilutive shares not used in calculating diluted weighted-average shares (in shares)	12,453	9,916	11,959	11,379