Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Income
Net income available to common stockholders	$ 36,679	$ 23,193
Diluted net income per share	$ 36,679	$ 23,193
Weighted-Average Shares
Net income available to common stockholders (in shares)	49,192,647	40,984,481
Effect of potentially dilutive stock options and restricted stock awards (in shares)	235,325	236,105
Diluted net income per share (in shares)	49,427,972	41,220,586
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.75	$ 0.57
Diluted net income per share (in dollars per share)	$ 0.74	$ 0.56