Stockholders' Equity - Reconciliation of beginning and ending common stock outstanding (Details) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of period	101,517,000
Balance, end of period	104,249,000
Common Stock [Member]
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of period	101,517,009	98,828,098
Issuance of common stock	2,446,136	2,493,171
Nonvested share-based awards, net	286,328	195,740
Balance, end of period	104,249,473