Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Determination of shares:
Weighted average basic shares outstanding (in shares)	116,293,000	91,191,000
Diluted weighted-average common shares outstanding (in shares)	118,595,000	94,650,000
Anti-dilutive securities, stock options (in shares)	1,940,633	646,307
Calculation of basic EPS:
Net income applicable to common stock	$ 40,992	$ 45,437
Weighted average basic shares outstanding (in shares)	116,293,000	91,191,000
Basic EPS (in dollars per share)	$ 0.35	$ 0.50
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 40,992	$ 45,437
Diluted weighted-average common shares outstanding (in shares)	118,595,000	94,650,000
Diluted EPS (in dollars per share)	$ 0.35	$ 0.48
Stock options
Determination of shares:
Assumed conversion of dilutive employee stock-based awards and restricted stock (in shares)	2,049,000	3,260,000
Restricted stock
Determination of shares:
Assumed conversion of dilutive employee stock-based awards and restricted stock (in shares)	253,000	199,000