Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Determination of shares:
Weighted average basic shares outstanding (in shares)	115,982,000	91,468,000	116,137,000	91,330,000
Diluted weighted-average common shares outstanding (in shares)	117,676,000	94,995,000	118,161,000	94,834,000
Anti-dilutive securities, stock options (in shares)	1,955,220	660,958	1,947,967	653,673
Calculation of basic EPS:
Net income applicable to common stock	$ 51,547	$ 53,988	$ 92,539	$ 99,425
Weighted average basic shares outstanding (in shares)	115,982,000	91,468,000	116,137,000	91,330,000
Basic EPS (in dollars per share)	$ 0.44	$ 0.59	$ 0.80	$ 1.09
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 51,547	$ 53,988	$ 92,539	$ 99,425
Diluted weighted-average common shares outstanding (in shares)	117,676,000	94,995,000	118,161,000	94,834,000
Diluted EPS (in dollars per share)	$ 0.44	$ 0.57	$ 0.78	$ 1.05
Stock options
Determination of shares:
Assumed conversion of dilutive employee stock-based awards and restricted stock (in shares)	1,598,000	3,319,000	1,832,000	3,299,000
Restricted stock
Determination of shares:
Assumed conversion of dilutive employee stock-based awards and restricted stock (in shares)	96,000	208,000	192,000	205,000