Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Income
Net income available to common stockholders	$ 41,113	$ 24,358	$ 117,426	$ 71,687
Diluted net income per share	$ 41,113	$ 24,358	$ 117,426	$ 71,687
Weighted-Average Shares
Net income available to common stockholders (in shares)	49,286,945	48,431,880	49,244,403	43,845,675
Effect of potentially dilutive stock options and restricted stock awards (in shares)	205,074	211,894	213,782	217,544
Diluted net income per share (in shares)	49,492,019	48,643,774	49,458,185	44,063,219
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.83	$ 0.50	$ 2.38	$ 1.64
Diluted net income per share (in dollars per share)	$ 0.83	$ 0.50	$ 2.37	$ 1.63