Stockholders' Equity - Reconciliation of beginning and ending common stock outstanding (Details) - shares	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of period	116,417,000
Balance, end of period	116,545,000	116,417,000
Common Stock
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of period	116,416,900	101,517,009
Issuance of common stock	41,020	14,063,100
Nonvested share-based awards, net of withheld shares	87,034	836,791
Balance, end of period	116,544,954	116,416,900