Capital Stock (Tables)

12 Months Ended

Dec. 31, 2017

Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]

Common Shares Outstanding and Treasury Shares Held Rollforward Table

Common Shares Outstanding	Year Ended December 31,
	2017	2016	2015
At beginning of period	114,985,072	80,256,544	79,649,946
Exercise of common stock options, net	—	636,937	67,808
Grants of restricted stock, net	892,632	281,591	538,790
Issuance of common stock	—	33,810,000	—
At end of period	115,877,704	114,985,072	80,256,544

Treasury Shares Held	Year Ended December 31,
	2017	2016	2015
At beginning of period	2,536,421	2,281,495	2,224,285
Shares received upon exercise of common stock options	—	13,854	36,818
Shares received upon vesting of restricted stock, net	101,672	241,072	20,392
At end of period	2,638,093	2,536,421	2,281,495